9.4 Reader

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The reader is a cursor over a borrowed buffer — stack-allocatable, no heap, no free. It decodes one value at a time, advancing the cursor.

struct peios_mp_reader { uint64_t _opaque[4]; };   /* opaque — do not inspect */

void   peios_mp_reader_init(struct peios_mp_reader *r, const void *buf, size_t len);
size_t peios_mp_reader_remaining(const struct peios_mp_reader *r);

Declare a struct peios_mp_reader locally and peios_mp_reader_init it over your buffer before use. buf may be NULL only when len is zero. Borrowed str/bin/ext pointers the reader hands back point into the original buffer and are valid for as long as it lives. peios_mp_reader_remaining reports the unconsumed byte count.

9.4.0.1 Peeking #

enum peios_mp_type {
    PEIOS_MP_NIL, PEIOS_MP_BOOL, PEIOS_MP_INT, PEIOS_MP_FLOAT,
    PEIOS_MP_STR, PEIOS_MP_BIN, PEIOS_MP_ARRAY, PEIOS_MP_MAP, PEIOS_MP_EXT,
};

int peios_mp_peek(const struct peios_mp_reader *r);

peios_mp_peek returns the peios_mp_type of the next value without consuming it, or -1 at end-of-input or on an invalid lead byte. Note that integers of every width and sign report as PEIOS_MP_INT — read them with peios_mp_read_int or peios_mp_read_uint as you prefer. Peek is how you drive a dispatch over a value whose type you don't know ahead of time.

9.4.0.2 Reading scalars #

int peios_mp_read_nil(struct peios_mp_reader *r);
int peios_mp_read_bool(struct peios_mp_reader *r, bool *out);
int peios_mp_read_int(struct peios_mp_reader *r, int64_t *out);
int peios_mp_read_uint(struct peios_mp_reader *r, uint64_t *out);
int peios_mp_read_float(struct peios_mp_reader *r, double *out);

Each consumes one value on success (returns 0) and leaves the cursor untouched on a type mismatch or truncation (-1 with errno == EINVAL) — so a failed read is safe to follow with a different-typed read or a peek. The out pointer is optional: pass NULL to consume/type-check a value without receiving its payload.

9.4.0.3 Reading strings, bytes, containers, extensions #

ssize_t peios_mp_read_str(struct peios_mp_reader *r, const char **out);
ssize_t peios_mp_read_bin(struct peios_mp_reader *r, const void **out);
ssize_t peios_mp_read_array(struct peios_mp_reader *r);
ssize_t peios_mp_read_map(struct peios_mp_reader *r);
ssize_t peios_mp_read_ext(struct peios_mp_reader *r, int8_t *type_out, const void **out);
int     peios_mp_skip(struct peios_mp_reader *r);

• peios_mp_read_str / peios_mp_read_bin borrow the bytes (a pointer into the reader's buffer via out) and return the length, or -1. Strings are not NUL-terminated — use the length — and peios_mp_read_str rejects invalid UTF-8.
• peios_mp_read_array returns the element count; peios_mp_read_map returns the key/value pair count (so read 2 * count values). After the header you read that many values yourself.
• peios_mp_read_ext borrows an extension value's bytes, reporting its signed type id through type_out (both type_out and out are independently optional), and returns the data length.
• peios_mp_skip consumes exactly one complete value, descending into nested containers — the way to ignore a value (or a whole subtree) you don't care about. 0 / -1.

struct peios_mp_reader r;
peios_mp_reader_init(&r, payload, payload_len);

ssize_t pairs = peios_mp_read_map(&r);          /* top-level map */
for (ssize_t i = 0; i < pairs; i++) {
    const char *key; ssize_t klen = peios_mp_read_str(&r, &key);
    /* dispatch on key… then read or skip the value */
    peios_mp_skip(&r);
}

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