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Be clearer about when jsonapi's need_escapes is needed

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Most operations beyond pure json parsing need to set need_escapes to
true to get access to field names and string scalars. Document this
fact more explicitly.

Slightly tweaked patch from:

Author: Corey Huinker <corey.huinker@gmail.com>

Discussion: https://postgr.es/m/CADkLM=c49Vkfg2+A8ubSuEtaGEjuaKZXCA6SrXA8kdwHjx3uxQ@mail.gmail.com
This commit is contained in:
Andrew Dunstan 2025-01-19 09:09:58 -05:00
parent d3d0983169
commit ea5ff5833c
2 changed files with 18 additions and 3 deletions
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6
src/common/jsonapi.c
View File

@ -1297,7 +1297,10 @@ parse_scalar(JsonLexContext *lex, const JsonSemAction *sem)
return result;
}
/* invoke the callback, which may take ownership of val */
/*
* invoke the callback, which may take ownership of val. For string
* values, val is NULL if need_escapes is false.
*/
result = (*sfunc) (sem->semstate, val, tok);
if (lex->flags & JSONLEX_CTX_OWNS_TOKENS)
@ -1326,6 +1329,7 @@ parse_object_field(JsonLexContext *lex, const JsonSemAction *sem)
return report_parse_error(JSON_PARSE_STRING, lex);
if ((ostart != NULL || oend != NULL) && lex->need_escapes)
{
/* fname is NULL if need_escapes is false */
fname = STRDUP(lex->strval->data);
if (fname == NULL)
return JSON_OUT_OF_MEMORY;

15
src/include/common/jsonapi.h
View File

@ -118,6 +118,12 @@ typedef struct JsonLexContext
struct jsonapi_StrValType *errormsg;
} JsonLexContext;
/*
* Function types for custom json parsing actions.
*
* fname will be NULL if the context has need_escapes=false, as will token for
* string type values.
*/
typedef JsonParseErrorType (*json_struct_action) (void *state);
typedef JsonParseErrorType (*json_ofield_action) (void *state, char *fname, bool isnull);
typedef JsonParseErrorType (*json_aelem_action) (void *state, bool isnull);
@ -197,12 +203,17 @@ extern JsonParseErrorType json_count_array_elements(JsonLexContext *lex,
* struct is allocated.
*
* If need_escapes is true, ->strval stores the unescaped lexemes.
*
* Setting need_escapes to true is necessary if the operation needs
* to reference field names or scalar string values. This is true of most
* operations beyond purely checking the json-validity of the source
* document.
*
* Unescaping is expensive, so only request it when necessary.
*
* If need_escapes is true or lex was given as NULL, then the caller is
* responsible for freeing the returned struct, either by calling
* freeJsonLexContext() or (in backend environment) via memory context
* cleanup.
* freeJsonLexContext() or (in backends) via memory context cleanup.
*/
extern JsonLexContext *makeJsonLexContextCstringLen(JsonLexContext *lex,
const char *json,