brkyvz commented on code in PR #585:
URL: https://github.com/apache/parquet-format/pull/585#discussion_r3632350959
##########
LogicalTypes.md:
##########
@@ -635,7 +635,183 @@ The type has two type parameters:
The sort order used for `GEOGRAPHY` is undefined. When writing data, no min/max
statistics should be saved for this type and if such non-compliant statistics
-are found during reading, they must be ignored.
+are found during reading, they must be ignored.
+
+### FILE
+
+`FILE` annotates a group that represents a reference to a range of bytes,
which may
+be stored inline in the value, elsewhere within the current file, or in an
external file. It
+is intended for use cases such as storing file inventories, manifests, and
unstructured
+data references (e.g., images or audio files stored in object storage).
+
+The annotated group may contain the following fields, identified by name case
sensitively,
+not by field order. Field IDs, if they exist, may also be used for projection.
Every field
+is optional both in the schema and in the data: a writer may omit any field
from the group
+definition, and any field that is present has a field repetition type of
`OPTIONAL`.
+A group need only define the fields it uses (for example, an inline-only group
may define
+just `inline`, and an external reference may define just `path`).
+
+| Field | Type |
+|----------------|------------|
+| `path` | STRING |
+| `offset` | INT64 |
+| `size` | INT64 |
+| `content_type` | STRING |
+| `checksum` | STRING |
+| `inline` | BYTE_ARRAY |
+
+A value resolves to bytes determined by `inline` / `path` / `offset` / `size`;
+`content_type` and `checksum` are metadata describing whatever is resolved.
+
+#### Fields
+
+For the descriptions below, a field is *set* when it is present in the `FILE`
group
+and its value is non-null (and, for string fields, non-empty[1]). A field is
*not set*
+when it is absent from the group, or is present but null or empty.
+
+[1] Implementations are not expected to treat empty strings as null
+
+##### path
+
+A URI-reference as defined by RFC 3986, encoded as a Parquet STRING (e.g.,
`s3://bucket/file.jpg`).
+The URI may be absolute or relative. No additional encoding (e.g., URI
encoding) is applied on top
+of the user-provided data. If `path` is not set, the value refers to the
current file
+(a self-reference).
+
+##### offset
+
+A byte offset indicating the start of the byte range within the referenced
data.
+If not set, readers must treat the value as 0.
+If set and non-zero, readers must seek to this offset to retrieve the
referenced data.
+`offset` must be set for a self-reference (`path` not set); it is optional for
an
+external reference (`path` set). `offset` must not be < 0.
+
+##### size
+
+The byte length of the referenced data. Must be zero or a positive integer if
set; a
+value of 0 indicates empty referenced data. `size` must be set whenever
`offset` is set.
+It may be omitted only for a whole-file external reference (`path` set,
`offset` not set),
+in which case the range runs to the end of the referenced file. Because a
self-reference
+always sets `offset`, it always sets `size` as well.
+
+##### content_type
+
+The media type (MIME type), as defined by RFC 2046, of the resolved bytes
(e.g., `image/png`).
+When not set, the type can be assumed as `application/octet-stream`.
+
+##### checksum
+
+A self-describing integrity token for the resolved bytes, of the form
+`<algorithm>:<digest>`, where `<digest>` is encoded according to the `Encoding`
+column below. Readers should ignore unknown algorithms. The recognized
algorithms
+are:
+
+| Algorithm | Encoding | Notes
|
+|-----------|---------------|----------------------------------------------------------|
+| `ETAG` | opaque | the object-store eTag, not recomputable
|
+| `MD5` | lowercase hex | as defined in RFC 6151 represented as 32 hex
characters |
+| `CRC32` | lowercase hex | as defined in RFC 3385, represented as 8 hex
characters |
+| `CRC32C` | lowercase hex | as defined in RFC 9260, represented as 8 hex
characters |
+| `SHA-256` | lowercase hex | as defined in RFC 6234, represented as 64 hex
characters |
+
+`<digest>` encodings are:
+
+* `lowercase hex`: the digest bytes rendered as lowercase hexadecimal, two
+ characters per byte and no separators (e.g.
`MD5:d41d8cd98f00b204e9800998ecf8427e`).
+* `opaque`: the token supplied verbatim by the object store, used only for
+ equality comparison and not otherwise interpreted.
+
+`checksum` applies to the resolved bytes, except for `ETAG`, which is the
+object-store eTag for the whole file referenced by `path`.
+
+##### inline
+
+The referenced bytes stored inline in the value. If `inline` is set, it
supplies the
+bytes and any locator fields (`path`, `offset`, `size`) that are set are
provenance
+only.
+
+#### Resolution
+
+A value resolves to bytes based on which of `inline`, `path`, `offset`, and
`size` are
+set:
+
+| `inline` | `path` | `offset` | `size` | Resolves to
|
+|----------|--------|----------|--------|-------------------------------------------------------|
+| set | – | – | – | the inline bytes
|
+| – | set | – | – | whole external file at `path`
|
+| – | set | set | - | invalid
|
+| – | set | – | set | external `path`, `[0, size)`
|
+| – | set | set | set | external `path`, `[offset, offset +
size)` |
+| – | - | set | - | invalid
|
+| – | - | - | set | invalid
|
+| – | – | set | set | this file, `[offset, offset + size)`
(self-reference) |
+| – | – | – | – | nothing — invalid
|
Review Comment:
fixed
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