| ===================== |
| Nanopb: API reference |
| ===================== |
| |
| .. include :: menu.rst |
| |
| .. contents :: |
| |
| |
| |
| |
| Compilation options |
| =================== |
| The following options can be specified in one of two ways: |
| |
| 1. Using the -D switch on the C compiler command line. |
| 2. By #defining them at the top of pb.h. |
| |
| You must have the same settings for the nanopb library and all code that |
| includes pb.h. |
| |
| ============================ ================================================ |
| __BIG_ENDIAN__ Set this if your platform stores integers and |
| floats in big-endian format. Mixed-endian |
| systems (different layout for ints and floats) |
| are currently not supported. |
| PB_NO_PACKED_STRUCTS Disable packed structs. Increases RAM usage but |
| is necessary on some platforms that do not |
| support unaligned memory access. |
| PB_ENABLE_MALLOC Set this to enable dynamic allocation support |
| in the decoder. |
| PB_MAX_REQUIRED_FIELDS Maximum number of required fields to check for |
| presence. Default value is 64. Increases stack |
| usage 1 byte per every 8 fields. Compiler |
| warning will tell if you need this. |
| PB_FIELD_16BIT Add support for tag numbers > 255 and fields |
| larger than 255 bytes or 255 array entries. |
| Increases code size 3 bytes per each field. |
| Compiler error will tell if you need this. |
| PB_FIELD_32BIT Add support for tag numbers > 65535 and fields |
| larger than 65535 bytes or 65535 array entries. |
| Increases code size 9 bytes per each field. |
| Compiler error will tell if you need this. |
| PB_NO_ERRMSG Disables the support for error messages; only |
| error information is the true/false return |
| value. Decreases the code size by a few hundred |
| bytes. |
| PB_BUFFER_ONLY Disables the support for custom streams. Only |
| supports encoding and decoding with memory |
| buffers. Speeds up execution and decreases code |
| size slightly. |
| PB_OLD_CALLBACK_STYLE Use the old function signature (void\* instead |
| of void\*\*) for callback fields. This was the |
| default until nanopb-0.2.1. |
| PB_SYSTEM_HEADER Replace the standard header files with a single |
| header file. It should define all the required |
| functions and typedefs listed on the |
| `overview page`_. Value must include quotes, |
| for example *#define PB_SYSTEM_HEADER "foo.h"*. |
| ============================ ================================================ |
| |
| The PB_MAX_REQUIRED_FIELDS, PB_FIELD_16BIT and PB_FIELD_32BIT settings allow |
| raising some datatype limits to suit larger messages. Their need is recognized |
| automatically by C-preprocessor #if-directives in the generated .pb.h files. |
| The default setting is to use the smallest datatypes (least resources used). |
| |
| .. _`overview page`: index.html#compiler-requirements |
| |
| |
| Proto file options |
| ================== |
| The generator behaviour can be adjusted using these options, defined in the |
| 'nanopb.proto' file in the generator folder: |
| |
| ============================ ================================================ |
| max_size Allocated size for *bytes* and *string* fields. |
| max_count Allocated number of entries in arrays |
| (*repeated* fields). |
| int_size Override the integer type of a field. |
| (To use e.g. uint8_t to save RAM.) |
| type Type of the generated field. Default value |
| is *FT_DEFAULT*, which selects automatically. |
| You can use *FT_CALLBACK*, *FT_POINTER*, |
| *FT_STATIC* or *FT_IGNORE* to force a callback |
| field, a dynamically allocated field, a static |
| field or to completely ignore the field. |
| long_names Prefix the enum name to the enum value in |
| definitions, i.e. *EnumName_EnumValue*. Enabled |
| by default. |
| packed_struct Make the generated structures packed. |
| NOTE: This cannot be used on CPUs that break |
| on unaligned accesses to variables. |
| skip_message Skip the whole message from generation. |
| no_unions Generate 'oneof' fields as optional fields |
| instead of C unions. |
| msgid Specifies a unique id for this message type. |
| Can be used by user code as an identifier. |
| ============================ ================================================ |
| |
| These options can be defined for the .proto files before they are converted |
| using the nanopb-generatory.py. There are three ways to define the options: |
| |
| 1. Using a separate .options file. |
| This is the preferred way as of nanopb-0.2.1, because it has the best |
| compatibility with other protobuf libraries. |
| 2. Defining the options on the command line of nanopb_generator.py. |
| This only makes sense for settings that apply to a whole file. |
| 3. Defining the options in the .proto file using the nanopb extensions. |
| This is the way used in nanopb-0.1, and will remain supported in the |
| future. It however sometimes causes trouble when using the .proto file |
| with other protobuf libraries. |
| |
| The effect of the options is the same no matter how they are given. The most |
| common purpose is to define maximum size for string fields in order to |
| statically allocate them. |
| |
| Defining the options in a .options file |
| --------------------------------------- |
| The preferred way to define options is to have a separate file |
| 'myproto.options' in the same directory as the 'myproto.proto'. :: |
| |
| # myproto.proto |
| message MyMessage { |
| required string name = 1; |
| repeated int32 ids = 4; |
| } |
| |
| :: |
| |
| # myproto.options |
| MyMessage.name max_size:40 |
| MyMessage.ids max_count:5 |
| |
| The generator will automatically search for this file and read the |
| options from it. The file format is as follows: |
| |
| * Lines starting with '#' or '//' are regarded as comments. |
| * Blank lines are ignored. |
| * All other lines should start with a field name pattern, followed by one or |
| more options. For example: *"MyMessage.myfield max_size:5 max_count:10"*. |
| * The field name pattern is matched against a string of form *'Message.field'*. |
| For nested messages, the string is *'Message.SubMessage.field'*. |
| * The field name pattern may use the notation recognized by Python fnmatch(): |
| |
| - *\** matches any part of string, like 'Message.\*' for all fields |
| - *\?* matches any single character |
| - *[seq]* matches any of characters 's', 'e' and 'q' |
| - *[!seq]* matches any other character |
| |
| * The options are written as *'option_name:option_value'* and several options |
| can be defined on same line, separated by whitespace. |
| * Options defined later in the file override the ones specified earlier, so |
| it makes sense to define wildcard options first in the file and more specific |
| ones later. |
| |
| If preferred, the name of the options file can be set using the command line |
| switch *-f* to nanopb_generator.py. |
| |
| Defining the options on command line |
| ------------------------------------ |
| The nanopb_generator.py has a simple command line option *-s OPTION:VALUE*. |
| The setting applies to the whole file that is being processed. |
| |
| Defining the options in the .proto file |
| --------------------------------------- |
| The .proto file format allows defining custom options for the fields. |
| The nanopb library comes with *nanopb.proto* which does exactly that, allowing |
| you do define the options directly in the .proto file:: |
| |
| import "nanopb.proto"; |
| |
| message MyMessage { |
| required string name = 1 [(nanopb).max_size = 40]; |
| repeated int32 ids = 4 [(nanopb).max_count = 5]; |
| } |
| |
| A small complication is that you have to set the include path of protoc so that |
| nanopb.proto can be found. This file, in turn, requires the file |
| *google/protobuf/descriptor.proto*. This is usually installed under |
| */usr/include*. Therefore, to compile a .proto file which uses options, use a |
| protoc command similar to:: |
| |
| protoc -I/usr/include -Inanopb/generator -I. -omessage.pb message.proto |
| |
| The options can be defined in file, message and field scopes:: |
| |
| option (nanopb_fileopt).max_size = 20; // File scope |
| message Message |
| { |
| option (nanopb_msgopt).max_size = 30; // Message scope |
| required string fieldsize = 1 [(nanopb).max_size = 40]; // Field scope |
| } |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| pb.h |
| ==== |
| |
| pb_type_t |
| --------- |
| Defines the encoder/decoder behaviour that should be used for a field. :: |
| |
| typedef uint8_t pb_type_t; |
| |
| The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data: |
| |
| ==================== ===== ================================================ |
| LTYPE identifier Value Storage format |
| ==================== ===== ================================================ |
| PB_LTYPE_VARINT 0x00 Integer. |
| PB_LTYPE_SVARINT 0x01 Integer, zigzag encoded. |
| PB_LTYPE_FIXED32 0x02 32-bit integer or floating point. |
| PB_LTYPE_FIXED64 0x03 64-bit integer or floating point. |
| PB_LTYPE_BYTES 0x04 Structure with *size_t* field and byte array. |
| PB_LTYPE_STRING 0x05 Null-terminated string. |
| PB_LTYPE_SUBMESSAGE 0x06 Submessage structure. |
| ==================== ===== ================================================ |
| |
| The bits 4-5 define whether the field is required, optional or repeated: |
| |
| ==================== ===== ================================================ |
| HTYPE identifier Value Field handling |
| ==================== ===== ================================================ |
| PB_HTYPE_REQUIRED 0x00 Verify that field exists in decoded message. |
| PB_HTYPE_OPTIONAL 0x10 Use separate *has_<field>* boolean to specify |
| whether the field is present. |
| (Unless it is a callback) |
| PB_HTYPE_REPEATED 0x20 A repeated field with preallocated array. |
| Separate *<field>_count* for number of items. |
| (Unless it is a callback) |
| ==================== ===== ================================================ |
| |
| The bits 6-7 define the how the storage for the field is allocated: |
| |
| ==================== ===== ================================================ |
| ATYPE identifier Value Allocation method |
| ==================== ===== ================================================ |
| PB_ATYPE_STATIC 0x00 Statically allocated storage in the structure. |
| PB_ATYPE_CALLBACK 0x40 A field with dynamic storage size. Struct field |
| actually contains a pointer to a callback |
| function. |
| ==================== ===== ================================================ |
| |
| |
| pb_field_t |
| ---------- |
| Describes a single structure field with memory position in relation to others. The descriptions are usually autogenerated. :: |
| |
| typedef struct _pb_field_t pb_field_t; |
| struct _pb_field_t { |
| uint8_t tag; |
| pb_type_t type; |
| uint8_t data_offset; |
| int8_t size_offset; |
| uint8_t data_size; |
| uint8_t array_size; |
| const void *ptr; |
| } pb_packed; |
| |
| :tag: Tag number of the field or 0 to terminate a list of fields. |
| :type: LTYPE, HTYPE and ATYPE of the field. |
| :data_offset: Offset of field data, relative to the end of the previous field. |
| :size_offset: Offset of *bool* flag for optional fields or *size_t* count for arrays, relative to field data. |
| :data_size: Size of a single data entry, in bytes. For PB_LTYPE_BYTES, the size of the byte array inside the containing structure. For PB_HTYPE_CALLBACK, size of the C data type if known. |
| :array_size: Maximum number of entries in an array, if it is an array type. |
| :ptr: Pointer to default value for optional fields, or to submessage description for PB_LTYPE_SUBMESSAGE. |
| |
| The *uint8_t* datatypes limit the maximum size of a single item to 255 bytes and arrays to 255 items. Compiler will give error if the values are too large. The types can be changed to larger ones by defining *PB_FIELD_16BIT*. |
| |
| pb_bytes_array_t |
| ---------------- |
| An byte array with a field for storing the length:: |
| |
| typedef struct { |
| size_t size; |
| uint8_t bytes[1]; |
| } pb_bytes_array_t; |
| |
| In an actual array, the length of *bytes* may be different. |
| |
| pb_callback_t |
| ------------- |
| Part of a message structure, for fields with type PB_HTYPE_CALLBACK:: |
| |
| typedef struct _pb_callback_t pb_callback_t; |
| struct _pb_callback_t { |
| union { |
| bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void **arg); |
| bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void * const *arg); |
| } funcs; |
| |
| void *arg; |
| }; |
| |
| A pointer to the *arg* is passed to the callback when calling. It can be used to store any information that the callback might need. |
| |
| Previously the function received just the value of *arg* instead of a pointer to it. This old behaviour can be enabled by defining *PB_OLD_CALLBACK_STYLE*. |
| |
| When calling `pb_encode`_, *funcs.encode* is used, and similarly when calling `pb_decode`_, *funcs.decode* is used. The function pointers are stored in the same memory location but are of incompatible types. You can set the function pointer to NULL to skip the field. |
| |
| pb_wire_type_t |
| -------------- |
| Protocol Buffers wire types. These are used with `pb_encode_tag`_. :: |
| |
| typedef enum { |
| PB_WT_VARINT = 0, |
| PB_WT_64BIT = 1, |
| PB_WT_STRING = 2, |
| PB_WT_32BIT = 5 |
| } pb_wire_type_t; |
| |
| pb_extension_type_t |
| ------------------- |
| Defines the handler functions and auxiliary data for a field that extends |
| another message. Usually autogenerated by *nanopb_generator.py*:: |
| |
| typedef struct { |
| bool (*decode)(pb_istream_t *stream, pb_extension_t *extension, |
| uint32_t tag, pb_wire_type_t wire_type); |
| bool (*encode)(pb_ostream_t *stream, const pb_extension_t *extension); |
| const void *arg; |
| } pb_extension_type_t; |
| |
| In the normal case, the function pointers are *NULL* and the decoder and |
| encoder use their internal implementations. The internal implementations |
| assume that *arg* points to a *pb_field_t* that describes the field in question. |
| |
| To implement custom processing of unknown fields, you can provide pointers |
| to your own functions. Their functionality is mostly the same as for normal |
| callback fields, except that they get called for any unknown field when decoding. |
| |
| pb_extension_t |
| -------------- |
| Ties together the extension field type and the storage for the field value:: |
| |
| typedef struct { |
| const pb_extension_type_t *type; |
| void *dest; |
| pb_extension_t *next; |
| } pb_extension_t; |
| |
| :type: Pointer to the structure that defines the callback functions. |
| :dest: Pointer to the variable that stores the field value |
| (as used by the default extension callback functions.) |
| :next: Pointer to the next extension handler, or *NULL*. |
| |
| PB_GET_ERROR |
| ------------ |
| Get the current error message from a stream, or a placeholder string if |
| there is no error message:: |
| |
| #define PB_GET_ERROR(stream) (string expression) |
| |
| This should be used for printing errors, for example:: |
| |
| if (!pb_decode(...)) |
| { |
| printf("Decode failed: %s\n", PB_GET_ERROR(stream)); |
| } |
| |
| The macro only returns pointers to constant strings (in code memory), |
| so that there is no need to release the returned pointer. |
| |
| PB_RETURN_ERROR |
| --------------- |
| Set the error message and return false:: |
| |
| #define PB_RETURN_ERROR(stream,msg) (sets error and returns false) |
| |
| This should be used to handle error conditions inside nanopb functions |
| and user callback functions:: |
| |
| if (error_condition) |
| { |
| PB_RETURN_ERROR(stream, "something went wrong"); |
| } |
| |
| The *msg* parameter must be a constant string. |
| |
| |
| |
| pb_encode.h |
| =========== |
| |
| pb_ostream_from_buffer |
| ---------------------- |
| Constructs an output stream for writing into a memory buffer. This is just a helper function, it doesn't do anything you couldn't do yourself in a callback function. It uses an internal callback that stores the pointer in stream *state* field. :: |
| |
| pb_ostream_t pb_ostream_from_buffer(uint8_t *buf, size_t bufsize); |
| |
| :buf: Memory buffer to write into. |
| :bufsize: Maximum number of bytes to write. |
| :returns: An output stream. |
| |
| After writing, you can check *stream.bytes_written* to find out how much valid data there is in the buffer. |
| |
| pb_write |
| -------- |
| Writes data to an output stream. Always use this function, instead of trying to call stream callback manually. :: |
| |
| bool pb_write(pb_ostream_t *stream, const uint8_t *buf, size_t count); |
| |
| :stream: Output stream to write to. |
| :buf: Pointer to buffer with the data to be written. |
| :count: Number of bytes to write. |
| :returns: True on success, false if maximum length is exceeded or an IO error happens. |
| |
| If an error happens, *bytes_written* is not incremented. Depending on the callback used, calling pb_write again after it has failed once may be dangerous. Nanopb itself never does this, instead it returns the error to user application. The builtin pb_ostream_from_buffer is safe to call again after failed write. |
| |
| pb_encode |
| --------- |
| Encodes the contents of a structure as a protocol buffers message and writes it to output stream. :: |
| |
| bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); |
| |
| :stream: Output stream to write to. |
| :fields: A field description array, usually autogenerated. |
| :src_struct: Pointer to the data that will be serialized. |
| :returns: True on success, false on IO error, on detectable errors in field description, or if a field encoder returns false. |
| |
| Normally pb_encode simply walks through the fields description array and serializes each field in turn. However, submessages must be serialized twice: first to calculate their size and then to actually write them to output. This causes some constraints for callback fields, which must return the same data on every call. |
| |
| pb_encode_delimited |
| ------------------- |
| Calculates the length of the message, encodes it as varint and then encodes the message. :: |
| |
| bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); |
| |
| (parameters are the same as for `pb_encode`_.) |
| |
| A common way to indicate the message length in Protocol Buffers is to prefix it with a varint. |
| This function does this, and it is compatible with *parseDelimitedFrom* in Google's protobuf library. |
| |
| .. sidebar:: Encoding fields manually |
| |
| The functions with names *pb_encode_\** are used when dealing with callback fields. The typical reason for using callbacks is to have an array of unlimited size. In that case, `pb_encode`_ will call your callback function, which in turn will call *pb_encode_\** functions repeatedly to write out values. |
| |
| The tag of a field must be encoded separately with `pb_encode_tag_for_field`_. After that, you can call exactly one of the content-writing functions to encode the payload of the field. For repeated fields, you can repeat this process multiple times. |
| |
| Writing packed arrays is a little bit more involved: you need to use `pb_encode_tag` and specify `PB_WT_STRING` as the wire type. Then you need to know exactly how much data you are going to write, and use `pb_encode_varint`_ to write out the number of bytes before writing the actual data. Substreams can be used to determine the number of bytes beforehand; see `pb_encode_submessage`_ source code for an example. |
| |
| pb_encode_tag |
| ------------- |
| Starts a field in the Protocol Buffers binary format: encodes the field number and the wire type of the data. :: |
| |
| bool pb_encode_tag(pb_ostream_t *stream, pb_wire_type_t wiretype, int field_number); |
| |
| :stream: Output stream to write to. 1-5 bytes will be written. |
| :wiretype: PB_WT_VARINT, PB_WT_64BIT, PB_WT_STRING or PB_WT_32BIT |
| :field_number: Identifier for the field, defined in the .proto file. You can get it from field->tag. |
| :returns: True on success, false on IO error. |
| |
| pb_encode_tag_for_field |
| ----------------------- |
| Same as `pb_encode_tag`_, except takes the parameters from a *pb_field_t* structure. :: |
| |
| bool pb_encode_tag_for_field(pb_ostream_t *stream, const pb_field_t *field); |
| |
| :stream: Output stream to write to. 1-5 bytes will be written. |
| :field: Field description structure. Usually autogenerated. |
| :returns: True on success, false on IO error or unknown field type. |
| |
| This function only considers the LTYPE of the field. You can use it from your field callbacks, because the source generator writes correct LTYPE also for callback type fields. |
| |
| Wire type mapping is as follows: |
| |
| ========================= ============ |
| LTYPEs Wire type |
| ========================= ============ |
| VARINT, SVARINT PB_WT_VARINT |
| FIXED64 PB_WT_64BIT |
| STRING, BYTES, SUBMESSAGE PB_WT_STRING |
| FIXED32 PB_WT_32BIT |
| ========================= ============ |
| |
| pb_encode_varint |
| ---------------- |
| Encodes a signed or unsigned integer in the varint_ format. Works for fields of type `bool`, `enum`, `int32`, `int64`, `uint32` and `uint64`:: |
| |
| bool pb_encode_varint(pb_ostream_t *stream, uint64_t value); |
| |
| :stream: Output stream to write to. 1-10 bytes will be written. |
| :value: Value to encode. Just cast e.g. int32_t directly to uint64_t. |
| :returns: True on success, false on IO error. |
| |
| .. _varint: http://code.google.com/apis/protocolbuffers/docs/encoding.html#varints |
| |
| pb_encode_svarint |
| ----------------- |
| Encodes a signed integer in the 'zig-zagged' format. Works for fields of type `sint32` and `sint64`:: |
| |
| bool pb_encode_svarint(pb_ostream_t *stream, int64_t value); |
| |
| (parameters are the same as for `pb_encode_varint`_ |
| |
| pb_encode_string |
| ---------------- |
| Writes the length of a string as varint and then contents of the string. Works for fields of type `bytes` and `string`:: |
| |
| bool pb_encode_string(pb_ostream_t *stream, const uint8_t *buffer, size_t size); |
| |
| :stream: Output stream to write to. |
| :buffer: Pointer to string data. |
| :size: Number of bytes in the string. Pass `strlen(s)` for strings. |
| :returns: True on success, false on IO error. |
| |
| pb_encode_fixed32 |
| ----------------- |
| Writes 4 bytes to stream and swaps bytes on big-endian architectures. Works for fields of type `fixed32`, `sfixed32` and `float`:: |
| |
| bool pb_encode_fixed32(pb_ostream_t *stream, const void *value); |
| |
| :stream: Output stream to write to. |
| :value: Pointer to a 4-bytes large C variable, for example `uint32_t foo;`. |
| :returns: True on success, false on IO error. |
| |
| pb_encode_fixed64 |
| ----------------- |
| Writes 8 bytes to stream and swaps bytes on big-endian architecture. Works for fields of type `fixed64`, `sfixed64` and `double`:: |
| |
| bool pb_encode_fixed64(pb_ostream_t *stream, const void *value); |
| |
| :stream: Output stream to write to. |
| :value: Pointer to a 8-bytes large C variable, for example `uint64_t foo;`. |
| :returns: True on success, false on IO error. |
| |
| pb_encode_submessage |
| -------------------- |
| Encodes a submessage field, including the size header for it. Works for fields of any message type:: |
| |
| bool pb_encode_submessage(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct); |
| |
| :stream: Output stream to write to. |
| :fields: Pointer to the autogenerated field description array for the submessage type, e.g. `MyMessage_fields`. |
| :src: Pointer to the structure where submessage data is. |
| :returns: True on success, false on IO errors, pb_encode errors or if submessage size changes between calls. |
| |
| In Protocol Buffers format, the submessage size must be written before the submessage contents. Therefore, this function has to encode the submessage twice in order to know the size beforehand. |
| |
| If the submessage contains callback fields, the callback function might misbehave and write out a different amount of data on the second call. This situation is recognized and *false* is returned, but garbage will be written to the output before the problem is detected. |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| pb_decode.h |
| =========== |
| |
| pb_istream_from_buffer |
| ---------------------- |
| Helper function for creating an input stream that reads data from a memory buffer. :: |
| |
| pb_istream_t pb_istream_from_buffer(uint8_t *buf, size_t bufsize); |
| |
| :buf: Pointer to byte array to read from. |
| :bufsize: Size of the byte array. |
| :returns: An input stream ready to use. |
| |
| pb_read |
| ------- |
| Read data from input stream. Always use this function, don't try to call the stream callback directly. :: |
| |
| bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count); |
| |
| :stream: Input stream to read from. |
| :buf: Buffer to store the data to, or NULL to just read data without storing it anywhere. |
| :count: Number of bytes to read. |
| :returns: True on success, false if *stream->bytes_left* is less than *count* or if an IO error occurs. |
| |
| End of file is signalled by *stream->bytes_left* being zero after pb_read returns false. |
| |
| pb_decode |
| --------- |
| Read and decode all fields of a structure. Reads until EOF on input stream. :: |
| |
| bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); |
| |
| :stream: Input stream to read from. |
| :fields: A field description array. Usually autogenerated. |
| :dest_struct: Pointer to structure where data will be stored. |
| :returns: True on success, false on IO error, on detectable errors in field description, if a field encoder returns false or if a required field is missing. |
| |
| In Protocol Buffers binary format, EOF is only allowed between fields. If it happens anywhere else, pb_decode will return *false*. If pb_decode returns false, you cannot trust any of the data in the structure. |
| |
| In addition to EOF, the pb_decode implementation supports terminating a message with a 0 byte. This is compatible with the official Protocol Buffers because 0 is never a valid field tag. |
| |
| For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present. |
| |
| If *PB_ENABLE_MALLOC* is defined, this function may allocate storage for any pointer type fields. |
| In this case, you have to call `pb_release`_ to release the memory after you are done with the message. |
| On error return `pb_decode` will release the memory itself. |
| |
| pb_decode_noinit |
| ---------------- |
| Same as `pb_decode`_, except does not apply the default values to fields. :: |
| |
| bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); |
| |
| (parameters are the same as for `pb_decode`_.) |
| |
| The destination structure should be filled with zeros before calling this function. Doing a *memset* manually can be slightly faster than using `pb_decode`_ if you don't need any default values. |
| |
| In addition to decoding a single message, this function can be used to merge two messages, so that |
| values from previous message will remain if the new message does not contain a field. |
| |
| This function *will not* release the message even on error return. If you use *PB_ENABLE_MALLOC*, |
| you will need to call `pb_release`_ yourself. |
| |
| pb_decode_delimited |
| ------------------- |
| Same as `pb_decode`_, except that it first reads a varint with the length of the message. :: |
| |
| bool pb_decode_delimited(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct); |
| |
| (parameters are the same as for `pb_decode`_.) |
| |
| A common method to indicate message size in Protocol Buffers is to prefix it with a varint. |
| This function is compatible with *writeDelimitedTo* in the Google's Protocol Buffers library. |
| |
| pb_release |
| ---------- |
| Releases any dynamically allocated fields. |
| |
| void pb_release(const pb_field_t fields[], void *dest_struct); |
| |
| :fields: A field description array. Usually autogenerated. |
| :dest_struct: Pointer to structure where data will be stored. |
| |
| This function is only available if *PB_ENABLE_MALLOC* is defined. It will release any |
| pointer type fields in the structure and set the pointers to NULL. |
| |
| pb_skip_varint |
| -------------- |
| Skip a varint_ encoded integer without decoding it. :: |
| |
| bool pb_skip_varint(pb_istream_t *stream); |
| |
| :stream: Input stream to read from. Will read 1 byte at a time until the MSB is clear. |
| :returns: True on success, false on IO error. |
| |
| pb_skip_string |
| -------------- |
| Skip a varint-length-prefixed string. This means skipping a value with wire type PB_WT_STRING. :: |
| |
| bool pb_skip_string(pb_istream_t *stream); |
| |
| :stream: Input stream to read from. |
| :returns: True on success, false on IO error or length exceeding uint32_t. |
| |
| pb_decode_tag |
| ------------- |
| Decode the tag that comes before field in the protobuf encoding:: |
| |
| bool pb_decode_tag(pb_istream_t *stream, pb_wire_type_t *wire_type, int *tag, bool *eof); |
| |
| :stream: Input stream to read from. |
| :wire_type: Pointer to variable where to store the wire type of the field. |
| :tag: Pointer to variable where to store the tag of the field. |
| :eof: Pointer to variable where to store end-of-file status. |
| :returns: True on success, false on error or EOF. |
| |
| When the message (stream) ends, this function will return false and set *eof* to true. On other |
| errors, *eof* will be set to false. |
| |
| pb_skip_field |
| ------------- |
| Remove the data for a field from the stream, without actually decoding it:: |
| |
| bool pb_skip_field(pb_istream_t *stream, pb_wire_type_t wire_type); |
| |
| :stream: Input stream to read from. |
| :wire_type: Type of field to skip. |
| :returns: True on success, false on IO error. |
| |
| .. sidebar:: Decoding fields manually |
| |
| The functions with names beginning with *pb_decode_* are used when dealing with callback fields. The typical reason for using callbacks is to have an array of unlimited size. In that case, `pb_decode`_ will call your callback function repeatedly, which can then store the values into e.g. filesystem in the order received in. |
| |
| For decoding numeric (including enumerated and boolean) values, use `pb_decode_varint`_, `pb_decode_svarint`_, `pb_decode_fixed32`_ and `pb_decode_fixed64`_. They take a pointer to a 32- or 64-bit C variable, which you may then cast to smaller datatype for storage. |
| |
| For decoding strings and bytes fields, the length has already been decoded. You can therefore check the total length in *stream->bytes_left* and read the data using `pb_read`_. |
| |
| Finally, for decoding submessages in a callback, simply use `pb_decode`_ and pass it the *SubMessage_fields* descriptor array. |
| |
| pb_decode_varint |
| ---------------- |
| Read and decode a varint_ encoded integer. :: |
| |
| bool pb_decode_varint(pb_istream_t *stream, uint64_t *dest); |
| |
| :stream: Input stream to read from. 1-10 bytes will be read. |
| :dest: Storage for the decoded integer. Value is undefined on error. |
| :returns: True on success, false if value exceeds uint64_t range or an IO error happens. |
| |
| pb_decode_svarint |
| ----------------- |
| Similar to `pb_decode_varint`_, except that it performs zigzag-decoding on the value. This corresponds to the Protocol Buffers *sint32* and *sint64* datatypes. :: |
| |
| bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest); |
| |
| (parameters are the same as `pb_decode_varint`_) |
| |
| pb_decode_fixed32 |
| ----------------- |
| Decode a *fixed32*, *sfixed32* or *float* value. :: |
| |
| bool pb_decode_fixed32(pb_istream_t *stream, void *dest); |
| |
| :stream: Input stream to read from. 4 bytes will be read. |
| :dest: Pointer to destination *int32_t*, *uint32_t* or *float*. |
| :returns: True on success, false on IO errors. |
| |
| This function reads 4 bytes from the input stream. |
| On big endian architectures, it then reverses the order of the bytes. |
| Finally, it writes the bytes to *dest*. |
| |
| pb_decode_fixed64 |
| ----------------- |
| Decode a *fixed64*, *sfixed64* or *double* value. :: |
| |
| bool pb_dec_fixed(pb_istream_t *stream, const pb_field_t *field, void *dest); |
| |
| :stream: Input stream to read from. 8 bytes will be read. |
| :field: Not used. |
| :dest: Pointer to destination *int64_t*, *uint64_t* or *double*. |
| :returns: True on success, false on IO errors. |
| |
| Same as `pb_decode_fixed32`_, except this reads 8 bytes. |
| |
| pb_make_string_substream |
| ------------------------ |
| Decode the length for a field with wire type *PB_WT_STRING* and create a substream for reading the data. :: |
| |
| bool pb_make_string_substream(pb_istream_t *stream, pb_istream_t *substream); |
| |
| :stream: Original input stream to read the length and data from. |
| :substream: New substream that has limited length. Filled in by the function. |
| :returns: True on success, false if reading the length fails. |
| |
| This function uses `pb_decode_varint`_ to read an integer from the stream. This is interpreted as a number of bytes, and the substream is set up so that its `bytes_left` is initially the same as the length, and its callback function and state the same as the parent stream. |
| |
| pb_close_string_substream |
| ------------------------- |
| Close the substream created with `pb_make_string_substream`_. :: |
| |
| void pb_close_string_substream(pb_istream_t *stream, pb_istream_t *substream); |
| |
| :stream: Original input stream to read the length and data from. |
| :substream: Substream to close |
| |
| This function copies back the state from the substream to the parent stream. |
| It must be called after done with the substream. |
