xet protocol files

.github/workflows/xet_build_documentation.yml

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+name: Build Xet documentation
+
+on:
+  push:
+    paths:
+      - "docs/xet/**"
+    branches:
+      - main
+
+jobs:
+   build:
+    uses: huggingface/doc-builder/.github/workflows/build_main_documentation.yml@main
+    with:
+      commit_sha: ${{ github.sha }}
+      package: hub-docs
+      package_name: xet
+      path_to_docs: hub-docs/docs/xet/
+      additional_args: --not_python_module
+    secrets:
+      hf_token: ${{ secrets.HF_DOC_BUILD_PUSH }}

.github/workflows/xet_build_pr_documentation.yml

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+name: Build Xet PR Documentation
+
+on:
+  pull_request:
+    paths:
+      - "docs/xet/**"
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    uses: huggingface/doc-builder/.github/workflows/build_pr_documentation.yml@main
+    with:
+      commit_sha: ${{ github.event.pull_request.head.sha }}
+      pr_number: ${{ github.event.number }}
+      package: hub-docs
+      package_name: xet
+      path_to_docs: hub-docs/docs/xet/
+      additional_args: --not_python_module

.github/workflows/xet_upload_pr_documentation.yml

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+name: Upload Xet PR Documentation
+
+on:
+  workflow_run:
+    workflows: ["Build Xet PR Documentation"]
+    types:
+      - completed
+
+jobs:
+  build:
+    uses: huggingface/doc-builder/.github/workflows/upload_pr_documentation.yml@main
+    with:
+      package_name: xet
+    secrets:
+      hf_token: ${{ secrets.HF_DOC_BUILD_PUSH }}
+      comment_bot_token: ${{ secrets.COMMENT_BOT_TOKEN }}

docs/xet/_toctree.yml

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+- local: index
+  title: Xet Protocol Specification
+
+- title: Building a client library for xet storage
+  sections:
+    - local: upload-protocol
+      title: Upload Protocol
+    - local: download-protocol
+      title: Download Protocol
+    - local: api
+      title: CAS API
+    - local: auth
+      title: Authentication and Authorization
+    - local: file-id
+      title: Hugging Face Hub Files Conversion to Xet File ID's
+
+- title: Overall Xet architecture
+  sections:
+    - local: chunking
+      title: Content-Defined Chunking
+    - local: hashing
+      title: Hashing Methods
+    - local: file-reconstruction
+      title: File Reconstruction
+    - local: xorb
+      title: Xorb Format
+    - local: shard
+      title: Shard Format
+    - local: deduplication
+      title: Deduplication

docs/xet/api.md

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+# CAS API Documentation
+
+This document describes the HTTP API endpoints used by the Content Addressable Storage (CAS) client to interact with the remote CAS server.
+
+## Authentication
+
+To authenticate, authorize, and obtain the API base URL, follow the instructions in [Authentication](./auth).
+
+## Converting Hashes to Strings
+
+Sometimes hashes are used in API paths as hexadecimal strings (reconstruction, xorb upload, global dedupe API).
+
+To convert a 32 hash to a 64 hexadecimal character string to be used as part of an API path there is a specific procedure, MUST NOT directly convert each byte.
+
+### Procedure
+
+For every 8 bytes in the hash (indices 0-7, 8-15, 16-23, 24-31) reverse the order of each byte in those regions then concatenate the regions back in order.
+
+Otherwise stated, consider each 8 byte part of a hash as a little endian 64 bit unsigned integer, then concatenate the hexadecimal representation of the 4 numbers in order (each padded with 0's to 16 characters).
+
+> [!NOTE]
+> In all cases that a hash is represented as a string it is converted from a byte array to a string using this procedure.
+
+### Example
+
+Suppose a hash value is:
+`[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]`
+
+Then before converting to a string it will first have its bytes reordered to:
+`[7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8, 23, 22, 21, 20, 19, 18, 17, 16, 31, 30, 29, 28, 27, 26, 25, 24]`
+
+So the string value of the the provided hash [0..32] is **NOT** `000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f`.
+It is: `07060504030201000f0e0d0c0b0a0908171615141312111f1e1d1c1b1a1918`.
+
+## Endpoints
+
+### 1. Get File Reconstruction
+
+- **Description**: Retrieves reconstruction information for a specific file, includes byte range support when `Range` header is set.
+- **Path**: `/v1/reconstructions/{file_id}`
+- **Method**: `GET`
+- **Parameters**:
+  - `file_id`: File hash in hex format (64 lowercase hexadecimal characters).
+See [file hashes](./hashing#file-hashes) for computing the file hash and [converting hashes to strings](./api#converting-hashes-to-strings).
+- **Headers**:
+  - `Range`: OPTIONAL. Format: `bytes={start}-{end}` (end is inclusive).
+- **Minimum Token Scope**: `read`
+- **Body**: None.
+- **Response**: JSON (`QueryReconstructionResponse`)
+
+  ```json
+  {
+    "offset_into_first_range": 0,
+    "terms": [...],
+    "fetch_info": {...}
+  }
+  ```
+
+- **Error Responses**: See [Error Cases](./api#error-cases)
+  - `400 Bad Request`: Malformed `file_id` in the path. Fix the path before retrying.
+  - `401 Unauthorized`: Refresh the token to continue making requests, or provide a token in the `Authorization` header.
+  - `404 Not Found`: The file does not exist. Not retryable.
+  - `416 Range Not Satisfiable`: The requested byte range start exceeds the end of the file. Not retryable.
+
+```txt
+GET /v1/reconstructions/0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+-H "Authorization: Bearer <token>"
+OPTIONAL: -H Range: "bytes=0-100000"
+```
+
+### Example File Reconstruction Response Body
+
+See [QueryReconstructionResponse](./download-protocol#queryreconstructionresponse-structure) for more details in the download protocol specification.
+
+### 2. Query Chunk Deduplication (Global Deduplication)
+
+- **Description**: Checks if a chunk exists in the CAS for deduplication purposes.
+- **Path**: `/v1/chunks/{prefix}/{hash}`
+- **Method**: `GET`
+- **Parameters**:
+  - `prefix`: The only acceptable prefix for the Global Deduplication API is `default-merkledb`.
+  - `hash`: Chunk hash in hex format (64 lowercase hexadecimal characters).
+See [Chunk Hashes](./hashing#chunk-hashes) to compute the chunk hash and [converting hashes to strings](./api#converting-hashes-to-strings).
+- **Minimum Token Scope**: `read`
+- **Body**: None.
+- **Response**: Shard format bytes (`application/octet-stream`), deserialize as a [shard](./shard#global-deduplication).
+- **Error Responses**: See [Error Cases](./api#error-cases)
+  - `400 Bad Request`: Malformed hash in the path. Fix the path before retrying.
+  - `401 Unauthorized`: Refresh the token to continue making requests, or provide a token in the `Authorization` header.
+  - `404 Not Found`: Chunk not already tracked by global deduplication. Not retryable.
+
+```txt
+GET /v1/chunks/default-merkledb/0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+-H "Authorization: Bearer <token>"
+```
+
+#### Example Shard Response Body
+
+An example shard response body can be found in [Xet reference files](https://huggingface.co/datasets/xet-team/xet-spec-reference-files/blob/main/Electric_Vehicle_Population_Data_20250917.csv.shard.dedupe).
+
+### 3. Upload Xorb
+
+- **Description**: Uploads a serialized Xorb to the server; uploading real data in serialized format.
+- **Path**: `/v1/xorbs/{prefix}/{hash}`
+- **Method**: `POST`
+- **Parameters**:
+  - `prefix`: The only acceptable prefix for the Xorb upload API is `default`.
+  - `hash`: Xorb hash in hex format (64 lowercase hexadecimal characters).
+See [Xorb Hashes](./hashing#xorb-hashes) to compute the hash, and [converting hashes to strings](./api#converting-hashes-to-strings).
+- **Minimum Token Scope**: `write`
+- **Body**: Serialized Xorb bytes (`application/octet-stream`).
+See [xorb format serialization](./xorb).
+- **Response**: JSON (`UploadXorbResponse`)
+
+```json
+{
+  "was_inserted": true
+}
+```
+
+- Note: `was_inserted` is `false` if the Xorb already exists; this is not an error.
+
+- **Error Responses**: See [Error Cases](./api#error-cases)
+  - `400 Bad Request`: Malformed hash in the path, Xorb hash does not match the body, or body is incorrectly serialized.
+  - `401 Unauthorized`: Refresh the token to continue making requests, or provide a token in the `Authorization` header.
+  - `403 Forbidden`: Token provided but does not have a wide enough scope (for example, a `read` token was provided). Clients MUST retry with a `write` scope token.
+
+```txt
+POST /v1/xorbs/default/0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
+-H "Authorization: Bearer <token>"
+```
+
+#### Example Xorb Request Body
+
+An example xorb request body can be found in [Xet reference files](https://huggingface.co/datasets/xet-team/xet-spec-reference-files/blob/main/eea25d6ee393ccae385820daed127b96ef0ea034dfb7cf6da3a950ce334b7632.xorb).
+
+### 4. Upload Shard
+
+- **Description**: Uploads a Shard to the CAS.
+Uploads file reconstructions and new xorb listing, serialized into the shard format; marks the files as uploaded.
+- **Path**: `/v1/shards`
+- **Method**: `POST`
+- **Minimum Token Scope**: `write`
+- **Body**: Serialized Shard data as bytes (`application/octet-stream`).
+See [Shard format guide](./shard#shard-upload).
+- **Response**: JSON (`UploadShardResponse`)
+
+```json
+{
+  "result": 0
+}
+```
+
+- Where `result` is:
+  - `0`: The Shard already exists.
+  - `1`: `SyncPerformed` — the Shard was registered.
+
+The value of `result` does not carry any meaning, if the upload shard API returns a `200 OK` status code, the upload was successful and the files listed are considered uploaded.
+
+- **Error Responses**: See [Error Cases](./api#error-cases)
+  - `400 Bad Request`: Shard is incorrectly serialized or Shard contents failed verification.
+    - Can mean that a referenced Xorb doesn't exist or the shard is too large
+  - `401 Unauthorized`: Refresh the token to continue making requests, or provide a token in the `Authorization` header.
+  - `403 Forbidden`: Token provided but does not have a wide enough scope (for example, a `read` token was provided).
+
+```txt
+POST /v1/shards
+-H "Authorization: Bearer <token>"
+```
+
+#### Example Shard Request Body
+
+An example shard request body can be found in [Xet reference files](https://huggingface.co/datasets/xet-team/xet-spec-reference-files/blob/main/Electric_Vehicle_Population_Data_20250917.csv.shard.verification-no-footer).
+
+## Error Cases
+
+### Non-Retryable Errors
+
+- **400 Bad Request**: Returned when the request parameters are invalid (for example, invalid Xorb/Shard on upload APIs).
+- **401 Unauthorized**: Refresh the token to continue making requests, or provide a token in the `Authorization` header.
+- **403 Forbidden**: Token provided but does not have a wide enough scope (for example, a `read` token was provided for an API requiring `write` scope).
+- **404 Not Found**: Occurs on `GET` APIs where the resource (Xorb, file) does not exist.
+- **416 Range Not Satisfiable**: Reconstruction API only; returned when byte range requests are invalid. Specifically, the requested start range is greater than or equal to the length of the file.
+
+### Retryable Errors
+
+- **Connection Errors**: Often caused by network issues. Retry if intermittent.
+Clients SHOULD ensure no firewall blocks requests and SHOULD NOT use DNS overrides.
+- **429 Rate Limiting**: Lower your request rate using a backoff strategy, then wait and retry.
+Assume all APIs are rate limited.
+- **500 Internal Server Error**: The server experienced an intermittent issue; clients SHOULD retry their requests.
+- **503 Service Unavailable**: Service is temporarily unable to process requests; wait and retry.
+- **504 Gateway Timeout**: Service took too long to respond; wait and retry.