DYNBUF.md (3763B)
1 <!-- 2 Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al. 3 4 SPDX-License-Identifier: curl 5 --> 6 7 # dynbuf 8 9 This is the internal module for creating and handling "dynamic buffers". This 10 means buffers that can be appended to, dynamically and grow to adapt. 11 12 There is always a terminating zero put at the end of the dynamic buffer. 13 14 The `struct dynbuf` is used to hold data for each instance of a dynamic 15 buffer. The members of that struct **MUST NOT** be accessed or modified 16 without using the dedicated dynbuf API. 17 18 ## `curlx_dyn_init` 19 20 ```c 21 void curlx_dyn_init(struct dynbuf *s, size_t toobig); 22 ``` 23 24 This initializes a struct to use for dynbuf and it cannot fail. The `toobig` 25 value **must** be set to the maximum size we allow this buffer instance to 26 grow to. The functions below return `CURLE_OUT_OF_MEMORY` when hitting this 27 limit. 28 29 ## `curlx_dyn_free` 30 31 ```c 32 void curlx_dyn_free(struct dynbuf *s); 33 ``` 34 35 Free the associated memory and clean up. After a free, the `dynbuf` struct can 36 be reused to start appending new data to. 37 38 ## `curlx_dyn_addn` 39 40 ```c 41 CURLcode curlx_dyn_addn(struct dynbuf *s, const void *mem, size_t len); 42 ``` 43 44 Append arbitrary data of a given length to the end of the buffer. 45 46 If this function fails it calls `curlx_dyn_free` on `dynbuf`. 47 48 ## `curlx_dyn_add` 49 50 ```c 51 CURLcode curlx_dyn_add(struct dynbuf *s, const char *str); 52 ``` 53 54 Append a C string to the end of the buffer. 55 56 If this function fails it calls `curlx_dyn_free` on `dynbuf`. 57 58 ## `curlx_dyn_addf` 59 60 ```c 61 CURLcode curlx_dyn_addf(struct dynbuf *s, const char *fmt, ...); 62 ``` 63 64 Append a `printf()`-style string to the end of the buffer. 65 66 If this function fails it calls `curlx_dyn_free` on `dynbuf`. 67 68 ## `curlx_dyn_vaddf` 69 70 ```c 71 CURLcode curlx_dyn_vaddf(struct dynbuf *s, const char *fmt, va_list ap); 72 ``` 73 74 Append a `vprintf()`-style string to the end of the buffer. 75 76 If this function fails it calls `curlx_dyn_free` on `dynbuf`. 77 78 ## `curlx_dyn_reset` 79 80 ```c 81 void curlx_dyn_reset(struct dynbuf *s); 82 ``` 83 84 Reset the buffer length, but leave the allocation. 85 86 ## `curlx_dyn_tail` 87 88 ```c 89 CURLcode curlx_dyn_tail(struct dynbuf *s, size_t length); 90 ``` 91 92 Keep `length` bytes of the buffer tail (the last `length` bytes of the 93 buffer). The rest of the buffer is dropped. The specified `length` must not be 94 larger than the buffer length. To instead keep the leading part, see 95 `curlx_dyn_setlen()`. 96 97 ## `curlx_dyn_ptr` 98 99 ```c 100 char *curlx_dyn_ptr(const struct dynbuf *s); 101 ``` 102 103 Returns a `char *` to the buffer if it has a length, otherwise may return 104 NULL. Since the buffer may be reallocated, this pointer should not be trusted 105 or used anymore after the next buffer manipulation call. 106 107 ## `curlx_dyn_uptr` 108 109 ```c 110 unsigned char *curlx_dyn_uptr(const struct dynbuf *s); 111 ``` 112 113 Returns an `unsigned char *` to the buffer if it has a length, otherwise may 114 return NULL. Since the buffer may be reallocated, this pointer should not be 115 trusted or used anymore after the next buffer manipulation call. 116 117 ## `curlx_dyn_len` 118 119 ```c 120 size_t curlx_dyn_len(const struct dynbuf *s); 121 ``` 122 123 Returns the length of the buffer in bytes. Does not include the terminating 124 zero byte. 125 126 ## `curlx_dyn_setlen` 127 128 ```c 129 CURLcode curlx_dyn_setlen(struct dynbuf *s, size_t len); 130 ``` 131 132 Sets the new shorter length of the buffer in number of bytes. Keeps the 133 leftmost set number of bytes, discards the rest. To instead keep the tail part 134 of the buffer, see `curlx_dyn_tail()`. 135 136 ## `curlx_dyn_take` 137 138 ```c 139 char *curlx_dyn_take(struct dynbuf *s, size_t *plen); 140 ``` 141 142 Transfers ownership of the internal buffer to the caller. The dynbuf 143 resets to its initial state. The returned pointer may be `NULL` if the 144 dynbuf never allocated memory. The returned length is the amount of 145 data written to the buffer. The actual allocated memory might be larger.