Line data    Source code

       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * stringinfo.h
       4             :  *    Declarations/definitions for "StringInfo" functions.
       5             :  *
       6             :  * StringInfo provides an extensible string data type (currently limited to a
       7             :  * length of 1GB).  It can be used to buffer either ordinary C strings
       8             :  * (null-terminated text) or arbitrary binary data.  All storage is allocated
       9             :  * with palloc() (falling back to malloc in frontend code).
      10             :  *
      11             :  * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
      12             :  * Portions Copyright (c) 1994, Regents of the University of California
      13             :  *
      14             :  * src/include/lib/stringinfo.h
      15             :  *
      16             :  *-------------------------------------------------------------------------
      17             :  */
      18             : #ifndef STRINGINFO_H
      19             : #define STRINGINFO_H
      20             : 
      21             : /*-------------------------
      22             :  * StringInfoData holds information about an extensible string.
      23             :  *      data    is the current buffer for the string.
      24             :  *      len     is the current string length.  Except in the case of read-only
      25             :  *              strings described below, there is guaranteed to be a
      26             :  *              terminating '\0' at data[len].
      27             :  *      maxlen  is the allocated size in bytes of 'data', i.e. the maximum
      28             :  *              string size (including the terminating '\0' char) that we can
      29             :  *              currently store in 'data' without having to reallocate
      30             :  *              more space.  We must always have maxlen > len, except
      31             :  *              in the read-only case described below.
      32             :  *      cursor  is initialized to zero by makeStringInfo, initStringInfo,
      33             :  *              initReadOnlyStringInfo and initStringInfoFromString but is not
      34             :  *              otherwise touched by the stringinfo.c routines.  Some routines
      35             :  *              use it to scan through a StringInfo.
      36             :  *
      37             :  * As a special case, a StringInfoData can be initialized with a read-only
      38             :  * string buffer.  In this case "data" does not necessarily point at a
      39             :  * palloc'd chunk, and management of the buffer storage is the caller's
      40             :  * responsibility.  maxlen is set to zero to indicate that this is the case.
      41             :  * Read-only StringInfoDatas cannot be appended to or reset.
      42             :  * Also, it is caller's option whether a read-only string buffer has a
      43             :  * terminating '\0' or not.  This depends on the intended usage.
      44             :  *-------------------------
      45             :  */
      46             : typedef struct StringInfoData
      47             : {
      48             :     char       *data;
      49             :     int         len;
      50             :     int         maxlen;
      51             :     int         cursor;
      52             : } StringInfoData;
      53             : 
      54             : typedef StringInfoData *StringInfo;
      55             : 
      56             : 
      57             : /*------------------------
      58             :  * There are four ways to create a StringInfo object initially:
      59             :  *
      60             :  * StringInfo stringptr = makeStringInfo();
      61             :  *      Both the StringInfoData and the data buffer are palloc'd.
      62             :  *
      63             :  * StringInfoData string;
      64             :  * initStringInfo(&string);
      65             :  *      The data buffer is palloc'd but the StringInfoData is just local.
      66             :  *      This is the easiest approach for a StringInfo object that will
      67             :  *      only live as long as the current routine.
      68             :  *
      69             :  * StringInfoData string;
      70             :  * initReadOnlyStringInfo(&string, existingbuf, len);
      71             :  *      The StringInfoData's data field is set to point directly to the
      72             :  *      existing buffer and the StringInfoData's len is set to the given len.
      73             :  *      The given buffer can point to memory that's not managed by palloc or
      74             :  *      is pointing partway through a palloc'd chunk.  The maxlen field is set
      75             :  *      to 0.  A read-only StringInfo cannot be appended to using any of the
      76             :  *      appendStringInfo functions or reset with resetStringInfo().  The given
      77             :  *      buffer can optionally omit the trailing NUL.
      78             :  *
      79             :  * StringInfoData string;
      80             :  * initStringInfoFromString(&string, palloced_buf, len);
      81             :  *      The StringInfoData's data field is set to point directly to the given
      82             :  *      buffer and the StringInfoData's len is set to the given len.  This
      83             :  *      method of initialization is useful when the buffer already exists.
      84             :  *      StringInfos initialized this way can be appended to using the
      85             :  *      appendStringInfo functions and reset with resetStringInfo().  The
      86             :  *      given buffer must be NUL-terminated.  The palloc'd buffer is assumed
      87             :  *      to be len + 1 in size.
      88             :  *
      89             :  * To destroy a StringInfo, pfree() the data buffer, and then pfree() the
      90             :  * StringInfoData if it was palloc'd.  For StringInfos created with
      91             :  * makeStringInfo(), destroyStringInfo() is provided for this purpose.
      92             :  * However, if the StringInfo was initialized using initReadOnlyStringInfo()
      93             :  * then the caller will need to consider if it is safe to pfree the data
      94             :  * buffer.
      95             :  *
      96             :  * NOTE: some routines build up a string using StringInfo, and then
      97             :  * release the StringInfoData but return the data string itself to their
      98             :  * caller.  At that point the data string looks like a plain palloc'd
      99             :  * string.
     100             :  *-------------------------
     101             :  */
     102             : 
     103             : /*------------------------
     104             :  * makeStringInfo
     105             :  * Create an empty 'StringInfoData' & return a pointer to it.
     106             :  */
     107             : extern StringInfo makeStringInfo(void);
     108             : 
     109             : /*------------------------
     110             :  * initStringInfo
     111             :  * Initialize a StringInfoData struct (with previously undefined contents)
     112             :  * to describe an empty string.
     113             :  */
     114             : extern void initStringInfo(StringInfo str);
     115             : 
     116             : /*------------------------
     117             :  * initReadOnlyStringInfo
     118             :  * Initialize a StringInfoData struct from an existing string without copying
     119             :  * the string.  The caller is responsible for ensuring the given string
     120             :  * remains valid as long as the StringInfoData does.  Calls to this are used
     121             :  * in performance critical locations where allocating a new buffer and copying
     122             :  * would be too costly.  Read-only StringInfoData's may not be appended to
     123             :  * using any of the appendStringInfo functions or reset with
     124             :  * resetStringInfo().
     125             :  *
     126             :  * 'data' does not need to point directly to a palloc'd chunk of memory and may
     127             :  * omit the NUL termination character at data[len].
     128             :  */
     129             : static inline void
     130      759858 : initReadOnlyStringInfo(StringInfo str, char *data, int len)
     131             : {
     132      759858 :     str->data = data;
     133      759858 :     str->len = len;
     134      759858 :     str->maxlen = 0;         /* read-only */
     135      759858 :     str->cursor = 0;
     136      759858 : }
     137             : 
     138             : /*------------------------
     139             :  * initStringInfoFromString
     140             :  * Initialize a StringInfoData struct from an existing string without copying
     141             :  * the string.  'data' must be a valid palloc'd chunk of memory that can have
     142             :  * repalloc() called should more space be required during a call to any of the
     143             :  * appendStringInfo functions.
     144             :  *
     145             :  * 'data' must be NUL terminated at 'len' bytes.
     146             :  */
     147             : static inline void
     148      506274 : initStringInfoFromString(StringInfo str, char *data, int len)
     149             : {
     150             :     Assert(data[len] == '\0');
     151             : 
     152      506274 :     str->data = data;
     153      506274 :     str->len = len;
     154      506274 :     str->maxlen = len + 1;
     155      506274 :     str->cursor = 0;
     156      506274 : }
     157             : 
     158             : /*------------------------
     159             :  * resetStringInfo
     160             :  * Clears the current content of the StringInfo, if any. The
     161             :  * StringInfo remains valid.
     162             :  */
     163             : extern void resetStringInfo(StringInfo str);
     164             : 
     165             : /*------------------------
     166             :  * appendStringInfo
     167             :  * Format text data under the control of fmt (an sprintf-style format string)
     168             :  * and append it to whatever is already in str.  More space is allocated
     169             :  * to str if necessary.  This is sort of like a combination of sprintf and
     170             :  * strcat.
     171             :  */
     172             : extern void appendStringInfo(StringInfo str, const char *fmt,...) pg_attribute_printf(2, 3);
     173             : 
     174             : /*------------------------
     175             :  * appendStringInfoVA
     176             :  * Attempt to format text data under the control of fmt (an sprintf-style
     177             :  * format string) and append it to whatever is already in str.  If successful
     178             :  * return zero; if not (because there's not enough space), return an estimate
     179             :  * of the space needed, without modifying str.  Typically the caller should
     180             :  * pass the return value to enlargeStringInfo() before trying again; see
     181             :  * appendStringInfo for standard usage pattern.
     182             :  */
     183             : extern int  appendStringInfoVA(StringInfo str, const char *fmt, va_list args) pg_attribute_printf(2, 0);
     184             : 
     185             : /*------------------------
     186             :  * appendStringInfoString
     187             :  * Append a null-terminated string to str.
     188             :  * Like appendStringInfo(str, "%s", s) but faster.
     189             :  */
     190             : extern void appendStringInfoString(StringInfo str, const char *s);
     191             : 
     192             : /*------------------------
     193             :  * appendStringInfoChar
     194             :  * Append a single byte to str.
     195             :  * Like appendStringInfo(str, "%c", ch) but much faster.
     196             :  */
     197             : extern void appendStringInfoChar(StringInfo str, char ch);
     198             : 
     199             : /*------------------------
     200             :  * appendStringInfoCharMacro
     201             :  * As above, but a macro for even more speed where it matters.
     202             :  * Caution: str argument will be evaluated multiple times.
     203             :  */
     204             : #define appendStringInfoCharMacro(str,ch) \
     205             :     (((str)->len + 1 >= (str)->maxlen) ? \
     206             :      appendStringInfoChar(str, ch) : \
     207             :      (void)((str)->data[(str)->len] = (ch), (str)->data[++(str)->len] = '\0'))
     208             : 
     209             : /*------------------------
     210             :  * appendStringInfoSpaces
     211             :  * Append a given number of spaces to str.
     212             :  */
     213             : extern void appendStringInfoSpaces(StringInfo str, int count);
     214             : 
     215             : /*------------------------
     216             :  * appendBinaryStringInfo
     217             :  * Append arbitrary binary data to a StringInfo, allocating more space
     218             :  * if necessary.
     219             :  */
     220             : extern void appendBinaryStringInfo(StringInfo str,
     221             :                                    const void *data, int datalen);
     222             : 
     223             : /*------------------------
     224             :  * appendBinaryStringInfoNT
     225             :  * Append arbitrary binary data to a StringInfo, allocating more space
     226             :  * if necessary. Does not ensure a trailing null-byte exists.
     227             :  */
     228             : extern void appendBinaryStringInfoNT(StringInfo str,
     229             :                                      const void *data, int datalen);
     230             : 
     231             : /*------------------------
     232             :  * enlargeStringInfo
     233             :  * Make sure a StringInfo's buffer can hold at least 'needed' more bytes.
     234             :  */
     235             : extern void enlargeStringInfo(StringInfo str, int needed);
     236             : 
     237             : /*------------------------
     238             :  * destroyStringInfo
     239             :  * Frees a StringInfo and its buffer (opposite of makeStringInfo()).
     240             :  */
     241             : extern void destroyStringInfo(StringInfo str);
     242             : 
     243             : #endif                          /* STRINGINFO_H */