jsonb.h

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/*-------------------------------------------------------------------------
 *
 * jsonb.h
 *    Declarations for jsonb data type support.
 *
 * Copyright (c) 1996-2017, PostgreSQL Global Development Group
 *
 * src/include/utils/jsonb.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef __JSONB_H__
#define __JSONB_H__

#include "lib/stringinfo.h"
#include "utils/array.h"
#include "utils/numeric.h"

/* Tokens used when sequentially processing a jsonb value */
typedef enum
{
    WJB_DONE,
    WJB_KEY,
    WJB_VALUE,
    WJB_ELEM,
    WJB_BEGIN_ARRAY,
    WJB_END_ARRAY,
    WJB_BEGIN_OBJECT,
    WJB_END_OBJECT
} JsonbIteratorToken;

/* Strategy numbers for GIN index opclasses */
#define JsonbContainsStrategyNumber     7
#define JsonbExistsStrategyNumber       9
#define JsonbExistsAnyStrategyNumber    10
#define JsonbExistsAllStrategyNumber    11

/*
 * In the standard jsonb_ops GIN opclass for jsonb, we choose to index both
 * keys and values.  The storage format is text.  The first byte of the text
 * string distinguishes whether this is a key (always a string), null value,
 * boolean value, numeric value, or string value.  However, array elements
 * that are strings are marked as though they were keys; this imprecision
 * supports the definition of the "exists" operator, which treats array
 * elements like keys.  The remainder of the text string is empty for a null
 * value, "t" or "f" for a boolean value, a normalized print representation of
 * a numeric value, or the text of a string value.  However, if the length of
 * this text representation would exceed JGIN_MAXLENGTH bytes, we instead hash
 * the text representation and store an 8-hex-digit representation of the
 * uint32 hash value, marking the prefix byte with an additional bit to
 * distinguish that this has happened.  Hashing long strings saves space and
 * ensures that we won't overrun the maximum entry length for a GIN index.
 * (But JGIN_MAXLENGTH is quite a bit shorter than GIN's limit.  It's chosen
 * to ensure that the on-disk text datum will have a short varlena header.)
 * Note that when any hashed item appears in a query, we must recheck index
 * matches against the heap tuple; currently, this costs nothing because we
 * must always recheck for other reasons.
 */
#define JGINFLAG_KEY    0x01    /* key (or string array element) */
#define JGINFLAG_NULL   0x02    /* null value */
#define JGINFLAG_BOOL   0x03    /* boolean value */
#define JGINFLAG_NUM    0x04    /* numeric value */
#define JGINFLAG_STR    0x05    /* string value (if not an array element) */
#define JGINFLAG_HASHED 0x10    /* OR'd into flag if value was hashed */
#define JGIN_MAXLENGTH  125     /* max length of text part before hashing */

/* Convenience macros */
#define DatumGetJsonb(d)    ((Jsonb *) PG_DETOAST_DATUM(d))
#define JsonbGetDatum(p)    PointerGetDatum(p)
#define PG_GETARG_JSONB(x)  DatumGetJsonb(PG_GETARG_DATUM(x))
#define PG_RETURN_JSONB(x)  PG_RETURN_POINTER(x)

typedef struct JsonbPair JsonbPair;
typedef struct JsonbValue JsonbValue;

/*
 * Jsonbs are varlena objects, so must meet the varlena convention that the
 * first int32 of the object contains the total object size in bytes.  Be sure
 * to use VARSIZE() and SET_VARSIZE() to access it, though!
 *
 * Jsonb is the on-disk representation, in contrast to the in-memory JsonbValue
 * representation.  Often, JsonbValues are just shims through which a Jsonb
 * buffer is accessed, but they can also be deep copied and passed around.
 *
 * Jsonb is a tree structure. Each node in the tree consists of a JEntry
 * header and a variable-length content (possibly of zero size).  The JEntry
 * header indicates what kind of a node it is, e.g. a string or an array,
 * and provides the length of its variable-length portion.
 *
 * The JEntry and the content of a node are not stored physically together.
 * Instead, the container array or object has an array that holds the JEntrys
 * of all the child nodes, followed by their variable-length portions.
 *
 * The root node is an exception; it has no parent array or object that could
 * hold its JEntry. Hence, no JEntry header is stored for the root node.  It
 * is implicitly known that the root node must be an array or an object,
 * so we can get away without the type indicator as long as we can distinguish
 * the two.  For that purpose, both an array and an object begin with a uint32
 * header field, which contains an JB_FOBJECT or JB_FARRAY flag.  When a naked
 * scalar value needs to be stored as a Jsonb value, what we actually store is
 * an array with one element, with the flags in the array's header field set
 * to JB_FSCALAR | JB_FARRAY.
 *
 * Overall, the Jsonb struct requires 4-bytes alignment. Within the struct,
 * the variable-length portion of some node types is aligned to a 4-byte
 * boundary, while others are not. When alignment is needed, the padding is
 * in the beginning of the node that requires it. For example, if a numeric
 * node is stored after a string node, so that the numeric node begins at
 * offset 3, the variable-length portion of the numeric node will begin with
 * one padding byte so that the actual numeric data is 4-byte aligned.
 */

/*
 * JEntry format.
 *
 * The least significant 28 bits store either the data length of the entry,
 * or its end+1 offset from the start of the variable-length portion of the
 * containing object.  The next three bits store the type of the entry, and
 * the high-order bit tells whether the least significant bits store a length
 * or an offset.
 *
 * The reason for the offset-or-length complication is to compromise between
 * access speed and data compressibility.  In the initial design each JEntry
 * always stored an offset, but this resulted in JEntry arrays with horrible
 * compressibility properties, so that TOAST compression of a JSONB did not
 * work well.  Storing only lengths would greatly improve compressibility,
 * but it makes random access into large arrays expensive (O(N) not O(1)).
 * So what we do is store an offset in every JB_OFFSET_STRIDE'th JEntry and
 * a length in the rest.  This results in reasonably compressible data (as
 * long as the stride isn't too small).  We may have to examine as many as
 * JB_OFFSET_STRIDE JEntrys in order to find out the offset or length of any
 * given item, but that's still O(1) no matter how large the container is.
 *
 * We could avoid eating a flag bit for this purpose if we were to store
 * the stride in the container header, or if we were willing to treat the
 * stride as an unchangeable constant.  Neither of those options is very
 * attractive though.
 */
typedef uint32 JEntry;

#define JENTRY_OFFLENMASK       0x0FFFFFFF
#define JENTRY_TYPEMASK         0x70000000
#define JENTRY_HAS_OFF          0x80000000

/* values stored in the type bits */
#define JENTRY_ISSTRING         0x00000000
#define JENTRY_ISNUMERIC        0x10000000
#define JENTRY_ISBOOL_FALSE     0x20000000
#define JENTRY_ISBOOL_TRUE      0x30000000
#define JENTRY_ISNULL           0x40000000
#define JENTRY_ISCONTAINER      0x50000000  /* array or object */

/* Access macros.  Note possible multiple evaluations */
#define JBE_OFFLENFLD(je_)      ((je_) & JENTRY_OFFLENMASK)
#define JBE_HAS_OFF(je_)        (((je_) & JENTRY_HAS_OFF) != 0)
#define JBE_ISSTRING(je_)       (((je_) & JENTRY_TYPEMASK) == JENTRY_ISSTRING)
#define JBE_ISNUMERIC(je_)      (((je_) & JENTRY_TYPEMASK) == JENTRY_ISNUMERIC)
#define JBE_ISCONTAINER(je_)    (((je_) & JENTRY_TYPEMASK) == JENTRY_ISCONTAINER)
#define JBE_ISNULL(je_)         (((je_) & JENTRY_TYPEMASK) == JENTRY_ISNULL)
#define JBE_ISBOOL_TRUE(je_)    (((je_) & JENTRY_TYPEMASK) == JENTRY_ISBOOL_TRUE)
#define JBE_ISBOOL_FALSE(je_)   (((je_) & JENTRY_TYPEMASK) == JENTRY_ISBOOL_FALSE)
#define JBE_ISBOOL(je_)         (JBE_ISBOOL_TRUE(je_) || JBE_ISBOOL_FALSE(je_))

/* Macro for advancing an offset variable to the next JEntry */
#define JBE_ADVANCE_OFFSET(offset, je) \
    do { \
        JEntry  je_ = (je); \
        if (JBE_HAS_OFF(je_)) \
            (offset) = JBE_OFFLENFLD(je_); \
        else \
            (offset) += JBE_OFFLENFLD(je_); \
    } while(0)

/*
 * We store an offset, not a length, every JB_OFFSET_STRIDE children.
 * Caution: this macro should only be referenced when creating a JSONB
 * value.  When examining an existing value, pay attention to the HAS_OFF
 * bits instead.  This allows changes in the offset-placement heuristic
 * without breaking on-disk compatibility.
 */
#define JB_OFFSET_STRIDE        32

/*
 * A jsonb array or object node, within a Jsonb Datum.
 *
 * An array has one child for each element, stored in array order.
 *
 * An object has two children for each key/value pair.  The keys all appear
 * first, in key sort order; then the values appear, in an order matching the
 * key order.  This arrangement keeps the keys compact in memory, making a
 * search for a particular key more cache-friendly.
 */
typedef struct JsonbContainer
{
    uint32      header;         /* number of elements or key/value pairs, and
                                 * flags */
    JEntry      children[FLEXIBLE_ARRAY_MEMBER];

    /* the data for each child node follows. */
} JsonbContainer;

/* flags for the header-field in JsonbContainer */
#define JB_CMASK                0x0FFFFFFF  /* mask for count field */
#define JB_FSCALAR              0x10000000  /* flag bits */
#define JB_FOBJECT              0x20000000
#define JB_FARRAY               0x40000000

/* convenience macros for accessing a JsonbContainer struct */
#define JsonContainerSize(jc)       ((jc)->header & JB_CMASK)
#define JsonContainerIsScalar(jc)   (((jc)->header & JB_FSCALAR) != 0)
#define JsonContainerIsObject(jc)   (((jc)->header & JB_FOBJECT) != 0)
#define JsonContainerIsArray(jc)    (((jc)->header & JB_FARRAY) != 0)

/* The top-level on-disk format for a jsonb datum. */
typedef struct
{
    int32       vl_len_;        /* varlena header (do not touch directly!) */
    JsonbContainer root;
} Jsonb;

/* convenience macros for accessing the root container in a Jsonb datum */
#define JB_ROOT_COUNT(jbp_)     (*(uint32 *) VARDATA(jbp_) & JB_CMASK)
#define JB_ROOT_IS_SCALAR(jbp_) ((*(uint32 *) VARDATA(jbp_) & JB_FSCALAR) != 0)
#define JB_ROOT_IS_OBJECT(jbp_) ((*(uint32 *) VARDATA(jbp_) & JB_FOBJECT) != 0)
#define JB_ROOT_IS_ARRAY(jbp_)  ((*(uint32 *) VARDATA(jbp_) & JB_FARRAY) != 0)


enum jbvType
{
    /* Scalar types */
    jbvNull = 0x0,
    jbvString,
    jbvNumeric,
    jbvBool,
    /* Composite types */
    jbvArray = 0x10,
    jbvObject,
    /* Binary (i.e. struct Jsonb) jbvArray/jbvObject */
    jbvBinary
};

/*
 * JsonbValue:  In-memory representation of Jsonb.  This is a convenient
 * deserialized representation, that can easily support using the "val"
 * union across underlying types during manipulation.  The Jsonb on-disk
 * representation has various alignment considerations.
 */
struct JsonbValue
{
    enum jbvType type;          /* Influences sort order */

    union
    {
        Numeric numeric;
        bool        boolean;
        struct
        {
            int         len;
            char       *val;    /* Not necessarily null-terminated */
        }           string;     /* String primitive type */

        struct
        {
            int         nElems;
            JsonbValue *elems;
            bool        rawScalar;  /* Top-level "raw scalar" array? */
        }           array;      /* Array container type */

        struct
        {
            int         nPairs; /* 1 pair, 2 elements */
            JsonbPair  *pairs;
        }           object;     /* Associative container type */

        struct
        {
            int         len;
            JsonbContainer *data;
        }           binary;     /* Array or object, in on-disk format */
    }           val;
};

#define IsAJsonbScalar(jsonbval)    ((jsonbval)->type >= jbvNull && \
                                     (jsonbval)->type <= jbvBool)

/*
 * Key/value pair within an Object.
 *
 * This struct type is only used briefly while constructing a Jsonb; it is
 * *not* the on-disk representation.
 *
 * Pairs with duplicate keys are de-duplicated.  We store the originally
 * observed pair ordering for the purpose of removing duplicates in a
 * well-defined way (which is "last observed wins").
 */
struct JsonbPair
{
    JsonbValue  key;            /* Must be a jbvString */
    JsonbValue  value;          /* May be of any type */
    uint32      order;          /* Pair's index in original sequence */
};

/* Conversion state used when parsing Jsonb from text, or for type coercion */
typedef struct JsonbParseState
{
    JsonbValue  contVal;
    Size        size;
    struct JsonbParseState *next;
} JsonbParseState;

/*
 * JsonbIterator holds details of the type for each iteration. It also stores a
 * Jsonb varlena buffer, which can be directly accessed in some contexts.
 */
typedef enum
{
    JBI_ARRAY_START,
    JBI_ARRAY_ELEM,
    JBI_OBJECT_START,
    JBI_OBJECT_KEY,
    JBI_OBJECT_VALUE
} JsonbIterState;

typedef struct JsonbIterator
{
    /* Container being iterated */
    JsonbContainer *container;
    uint32      nElems;         /* Number of elements in children array (will
                                 * be nPairs for objects) */
    bool        isScalar;       /* Pseudo-array scalar value? */
    JEntry     *children;       /* JEntrys for child nodes */
    /* Data proper.  This points to the beginning of the variable-length data */
    char       *dataProper;

    /* Current item in buffer (up to nElems) */
    int         curIndex;

    /* Data offset corresponding to current item */
    uint32      curDataOffset;

    /*
     * If the container is an object, we want to return keys and values
     * alternately; so curDataOffset points to the current key, and
     * curValueOffset points to the current value.
     */
    uint32      curValueOffset;

    /* Private state */
    JsonbIterState state;

    struct JsonbIterator *parent;
} JsonbIterator;


/* Support functions */
extern uint32 getJsonbOffset(const JsonbContainer *jc, int index);
extern uint32 getJsonbLength(const JsonbContainer *jc, int index);
extern int  compareJsonbContainers(JsonbContainer *a, JsonbContainer *b);
extern JsonbValue *findJsonbValueFromContainer(JsonbContainer *sheader,
                            uint32 flags,
                            JsonbValue *key);
extern JsonbValue *getIthJsonbValueFromContainer(JsonbContainer *sheader,
                              uint32 i);
extern JsonbValue *pushJsonbValue(JsonbParseState **pstate,
               JsonbIteratorToken seq, JsonbValue *jbVal);
extern JsonbIterator *JsonbIteratorInit(JsonbContainer *container);
extern JsonbIteratorToken JsonbIteratorNext(JsonbIterator **it, JsonbValue *val,
                  bool skipNested);
extern Jsonb *JsonbValueToJsonb(JsonbValue *val);
extern bool JsonbDeepContains(JsonbIterator **val,
                  JsonbIterator **mContained);
extern void JsonbHashScalarValue(const JsonbValue *scalarVal, uint32 *hash);

/* jsonb.c support functions */
extern char *JsonbToCString(StringInfo out, JsonbContainer *in,
               int estimated_len);
extern char *JsonbToCStringIndent(StringInfo out, JsonbContainer *in,
                     int estimated_len);


#endif                          /* __JSONB_H__ */