diff --git a/src/backend/replication/logical/proto.c b/src/backend/replication/logical/proto.c index d52c8963eb..ce9d5b4059 100644 --- a/src/backend/replication/logical/proto.c +++ b/src/backend/replication/logical/proto.c @@ -879,6 +879,7 @@ logicalrep_read_tuple(StringInfo in, LogicalRepTupleData *tuple) /* Read the data */ for (i = 0; i < natts; i++) { + char *buff; char kind; int len; StringInfo value = &tuple->colvalues[i]; @@ -899,19 +900,16 @@ logicalrep_read_tuple(StringInfo in, LogicalRepTupleData *tuple) len = pq_getmsgint(in, 4); /* read length */ /* and data */ - value->data = palloc(len + 1); - pq_copymsgbytes(in, value->data, len); + buff = palloc(len + 1); + pq_copymsgbytes(in, buff, len); /* * Not strictly necessary for LOGICALREP_COLUMN_BINARY, but * per StringInfo practice. */ - value->data[len] = '\0'; + buff[len] = '\0'; - /* make StringInfo fully valid */ - value->len = len; - value->cursor = 0; - value->maxlen = len; + initStringInfoFromString(value, buff, len); break; default: elog(ERROR, "unrecognized data representation type '%c'", kind); diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c index 597947410f..b574188d70 100644 --- a/src/backend/replication/logical/worker.c +++ b/src/backend/replication/logical/worker.c @@ -3582,10 +3582,7 @@ LogicalRepApplyLoop(XLogRecPtr last_received) /* Ensure we are reading the data into our memory context. */ MemoryContextSwitchTo(ApplyMessageContext); - s.data = buf; - s.len = len; - s.cursor = 0; - s.maxlen = -1; + initReadOnlyStringInfo(&s, buf, len); c = pq_getmsgbyte(&s); diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index c900427ecf..7c0355cb2d 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -1817,23 +1817,20 @@ exec_bind_message(StringInfo input_message) if (!isNull) { - const char *pvalue = pq_getmsgbytes(input_message, plength); + char *pvalue; /* - * Rather than copying data around, we just set up a phony + * Rather than copying data around, we just initialize a * StringInfo pointing to the correct portion of the message * buffer. We assume we can scribble on the message buffer so * as to maintain the convention that StringInfos have a * trailing null. This is grotty but is a big win when * dealing with very large parameter strings. */ - pbuf.data = unconstify(char *, pvalue); - pbuf.maxlen = plength + 1; - pbuf.len = plength; - pbuf.cursor = 0; - - csave = pbuf.data[plength]; - pbuf.data[plength] = '\0'; + pvalue = unconstify(char *, pq_getmsgbytes(input_message, plength)); + csave = pvalue[plength]; + pvalue[plength] = '\0'; + initReadOnlyStringInfo(&pbuf, pvalue, plength); } else { diff --git a/src/backend/utils/adt/rowtypes.c b/src/backend/utils/adt/rowtypes.c index ad176651d8..a941a76ff3 100644 --- a/src/backend/utils/adt/rowtypes.c +++ b/src/backend/utils/adt/rowtypes.c @@ -623,21 +623,19 @@ record_recv(PG_FUNCTION_ARGS) } else { + char *strbuff; + /* - * Rather than copying data around, we just set up a phony - * StringInfo pointing to the correct portion of the input buffer. - * We assume we can scribble on the input buffer so as to maintain - * the convention that StringInfos have a trailing null. + * Initialize a new StringInfo using the correct portion of the + * input buffer. We assume we can scribble on the input buffer so + * as to maintain the convention that StringInfos have a trailing + * null. */ - item_buf.data = &buf->data[buf->cursor]; - item_buf.maxlen = itemlen + 1; - item_buf.len = itemlen; - item_buf.cursor = 0; - + strbuff = &buf->data[buf->cursor]; buf->cursor += itemlen; - csave = buf->data[buf->cursor]; buf->data[buf->cursor] = '\0'; + initReadOnlyStringInfo(&item_buf, strbuff, itemlen); bufptr = &item_buf; nulls[i] = false; diff --git a/src/common/stringinfo.c b/src/common/stringinfo.c index 05b22b5c53..a6a05e2f91 100644 --- a/src/common/stringinfo.c +++ b/src/common/stringinfo.c @@ -70,10 +70,16 @@ initStringInfo(StringInfo str) * * Reset the StringInfo: the data buffer remains valid, but its * previous content, if any, is cleared. + * + * Read-only StringInfos as initialized by initReadOnlyStringInfo cannot be + * reset. */ void resetStringInfo(StringInfo str) { + /* Don't allow resets of read-only StringInfos */ + Assert(str->maxlen != 0); + str->data[0] = '\0'; str->len = 0; str->cursor = 0; @@ -284,6 +290,9 @@ enlargeStringInfo(StringInfo str, int needed) { int newlen; + /* Validate this is not a read-only StringInfo */ + Assert(str->maxlen != 0); + /* * Guard against out-of-range "needed" values. Without this, we can get * an overflow or infinite loop in the following. diff --git a/src/include/lib/stringinfo.h b/src/include/lib/stringinfo.h index 36a416f8e0..184fc1d522 100644 --- a/src/include/lib/stringinfo.h +++ b/src/include/lib/stringinfo.h @@ -27,10 +27,18 @@ * maxlen is the allocated size in bytes of 'data', i.e. the maximum * string size (including the terminating '\0' char) that we can * currently store in 'data' without having to reallocate - * more space. We must always have maxlen > len. - * cursor is initialized to zero by makeStringInfo or initStringInfo, - * but is not otherwise touched by the stringinfo.c routines. - * Some routines use it to scan through a StringInfo. + * more space. We must always have maxlen > len, except + * in the read-only case described below. + * cursor is initialized to zero by makeStringInfo, initStringInfo, + * initReadOnlyStringInfo and initStringInfoFromString but is not + * otherwise touched by the stringinfo.c routines. Some routines + * use it to scan through a StringInfo. + * + * As a special case, a StringInfoData can be initialized with a read-only + * string buffer. In this case "data" does not necessarily point at a + * palloc'd chunk, and management of the buffer storage is the caller's + * responsibility. maxlen is set to zero to indicate that this is the case. + * Read-only StringInfoDatas cannot be appended to or reset. *------------------------- */ typedef struct StringInfoData @@ -45,7 +53,7 @@ typedef StringInfoData *StringInfo; /*------------------------ - * There are two ways to create a StringInfo object initially: + * There are four ways to create a StringInfo object initially: * * StringInfo stringptr = makeStringInfo(); * Both the StringInfoData and the data buffer are palloc'd. @@ -56,8 +64,31 @@ typedef StringInfoData *StringInfo; * This is the easiest approach for a StringInfo object that will * only live as long as the current routine. * + * StringInfoData string; + * initReadOnlyStringInfo(&string, existingbuf, len); + * The StringInfoData's data field is set to point directly to the + * existing buffer and the StringInfoData's len is set to the given len. + * The given buffer can point to memory that's not managed by palloc or + * is pointing partway through a palloc'd chunk. The maxlen field is set + * to 0. A read-only StringInfo cannot be appended to using any of the + * appendStringInfo functions or reset with resetStringInfo(). The given + * buffer must be NUL-terminated. + * + * StringInfoData string; + * initStringInfoFromString(&string, palloced_buf, len); + * The StringInfoData's data field is set to point directly to the given + * buffer and the StringInfoData's len is set to the given len. This + * method of initialization is useful when the buffer already exists. + * StringInfos initialized this way can be appended to using the + * appendStringInfo functions and reset with resetStringInfo(). The + * given buffer must be NUL-terminated. The palloc'd buffer is assumed + * to be len + 1 in size. + * * To destroy a StringInfo, pfree() the data buffer, and then pfree() the * StringInfoData if it was palloc'd. There's no special support for this. + * However, if the StringInfo was initialized using initReadOnlyStringInfo() + * then the caller will need to consider if it is safe to pfree the data + * buffer. * * NOTE: some routines build up a string using StringInfo, and then * release the StringInfoData but return the data string itself to their @@ -79,6 +110,49 @@ extern StringInfo makeStringInfo(void); */ extern void initStringInfo(StringInfo str); +/*------------------------ + * initReadOnlyStringInfo + * Initialize a StringInfoData struct from an existing string without copying + * the string. The caller is responsible for ensuring the given string + * remains valid as long as the StringInfoData does. The given string must be + * NUL terminated at 'len' bytes. Calls to this are used in performance + * critical locations where allocating a new buffer and copying would be too + * costly. Read-only StringInfoData's may not be appended to using any of the + * appendStringInfo functions or reset with resetStringInfo(). + * + * 'data' does not need to point directly to a palloc'd chunk of memory. + */ +static inline void +initReadOnlyStringInfo(StringInfo str, char *data, int len) +{ + Assert(data[len] == '\0'); + + str->data = data; + str->len = len; + str->maxlen = 0; /* read-only */ + str->cursor = 0; +} + +/*------------------------ + * initStringInfoFromString + * Initialize a StringInfoData struct from an existing string without copying + * the string. 'data' must be a valid palloc'd chunk of memory that can have + * repalloc() called should more space be required during a call to any of the + * appendStringInfo functions. + * + * 'data' must be NUL terminated at 'len' bytes. + */ +static inline void +initStringInfoFromString(StringInfo str, char *data, int len) +{ + Assert(data[len] == '\0'); + + str->data = data; + str->len = len; + str->maxlen = len + 1; + str->cursor = 0; +} + /*------------------------ * resetStringInfo * Clears the current content of the StringInfo, if any. The