From a2e81892f7bd167538676122258be198c7343df7 Mon Sep 17 00:00:00 2001
From: oppiliappan <me@oppi.li>
Date: Thu, 29 Jan 2026 06:50:14 +0000
Subject: [PATCH] knotserver/xrpc: introduce sh.tangled.repo.tag to get a
 single tag

produces info about a single tag object

Signed-off-by: oppiliappan <me@oppi.li>
---
 api/tangled/repotag.go      | 33 ++++++++++++++
 knotserver/xrpc/repo_tag.go | 85 +++++++++++++++++++++++++++++++++++++
 knotserver/xrpc/xrpc.go     |  1 +
 lexicons/repo/tag.json      | 43 +++++++++++++++++++
 types/repo.go               |  4 ++
 5 files changed, 166 insertions(+)
 create mode 100644 api/tangled/repotag.go
 create mode 100644 knotserver/xrpc/repo_tag.go
 create mode 100644 lexicons/repo/tag.json

diff --git a/api/tangled/repotag.go b/api/tangled/repotag.go
new file mode 100644
index 00000000..e7e59cf7
--- /dev/null
+++ b/api/tangled/repotag.go
@@ -0,0 +1,33 @@
+// Code generated by cmd/lexgen (see Makefile's lexgen); DO NOT EDIT.
+
+package tangled
+
+// schema: sh.tangled.repo.tag
+
+import (
+	"bytes"
+	"context"
+
+	"github.com/bluesky-social/indigo/lex/util"
+)
+
+const (
+	RepoTagNSID = "sh.tangled.repo.tag"
+)
+
+// RepoTag calls the XRPC method "sh.tangled.repo.tag".
+//
+// repo: Repository identifier in format 'did:plc:.../repoName'
+// tag: Name of tag, such as v1.3.0
+func RepoTag(ctx context.Context, c util.LexClient, repo string, tag string) ([]byte, error) {
+	buf := new(bytes.Buffer)
+
+	params := map[string]interface{}{}
+	params["repo"] = repo
+	params["tag"] = tag
+	if err := c.LexDo(ctx, util.Query, "", "sh.tangled.repo.tag", params, nil, buf); err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
diff --git a/knotserver/xrpc/repo_tag.go b/knotserver/xrpc/repo_tag.go
new file mode 100644
index 00000000..3d7c2e34
--- /dev/null
+++ b/knotserver/xrpc/repo_tag.go
@@ -0,0 +1,85 @@
+package xrpc
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/object"
+
+	"tangled.org/core/knotserver/git"
+	"tangled.org/core/types"
+	xrpcerr "tangled.org/core/xrpc/errors"
+)
+
+func (x *Xrpc) RepoTag(w http.ResponseWriter, r *http.Request) {
+	repo := r.URL.Query().Get("repo")
+	repoPath, err := x.parseRepoParam(repo)
+	if err != nil {
+		writeError(w, err.(xrpcerr.XrpcError), http.StatusBadRequest)
+		return
+	}
+
+	tagName := r.URL.Query().Get("tag")
+	if tagName == "" {
+		writeError(w, xrpcerr.NewXrpcError(
+			xrpcerr.WithTag("InvalidRequest"),
+			xrpcerr.WithMessage("missing name parameter"),
+		), http.StatusBadRequest)
+		return
+	}
+
+	gr, err := git.PlainOpen(repoPath)
+	if err != nil {
+		x.Logger.Error("failed to open", "error", err)
+		writeError(w, xrpcerr.RepoNotFoundError, http.StatusNoContent)
+		return
+	}
+
+	// if this is not already formatted as refs/tags/v0.1.0, then format it
+	if !plumbing.ReferenceName(tagName).IsTag() {
+		tagName = plumbing.NewTagReferenceName(tagName).String()
+	}
+
+	tags, err := gr.Tags(&git.TagsOptions{
+		Pattern: tagName,
+	})
+
+	if len(tags) != 1 {
+		writeError(w, xrpcerr.NewXrpcError(
+			xrpcerr.WithTag("TagNotFound"),
+			xrpcerr.WithMessage(fmt.Sprintf("expected 1 tag to be returned, got %d tags", len(tags))),
+		), http.StatusBadRequest)
+		return
+	}
+
+	tag := tags[0]
+
+	if err != nil {
+		x.Logger.Warn("getting tags", "error", err.Error())
+		tags = []object.Tag{}
+	}
+
+	var target *object.Tag
+	if tag.Target != plumbing.ZeroHash {
+		target = &tag
+	}
+	tr := types.TagReference{
+		Tag: target,
+	}
+
+	tr.Reference = types.Reference{
+		Name: tag.Name,
+		Hash: tag.Hash.String(),
+	}
+
+	if tag.Message != "" {
+		tr.Message = tag.Message
+	}
+
+	response := types.RepoTagResponse{
+		Tag: &tr,
+	}
+
+	writeJson(w, response)
+}
diff --git a/knotserver/xrpc/xrpc.go b/knotserver/xrpc/xrpc.go
index c110356f..940d543a 100644
--- a/knotserver/xrpc/xrpc.go
+++ b/knotserver/xrpc/xrpc.go
@@ -59,6 +59,7 @@ func (x *Xrpc) Router() http.Handler {
 	r.Get("/"+tangled.RepoLogNSID, x.RepoLog)
 	r.Get("/"+tangled.RepoBranchesNSID, x.RepoBranches)
 	r.Get("/"+tangled.RepoTagsNSID, x.RepoTags)
+	r.Get("/"+tangled.RepoTagNSID, x.RepoTag)
 	r.Get("/"+tangled.RepoBlobNSID, x.RepoBlob)
 	r.Get("/"+tangled.RepoDiffNSID, x.RepoDiff)
 	r.Get("/"+tangled.RepoCompareNSID, x.RepoCompare)
diff --git a/lexicons/repo/tag.json b/lexicons/repo/tag.json
new file mode 100644
index 00000000..06dfdf69
--- /dev/null
+++ b/lexicons/repo/tag.json
@@ -0,0 +1,43 @@
+{
+  "lexicon": 1,
+  "id": "sh.tangled.repo.tag",
+  "defs": {
+    "main": {
+      "type": "query",
+      "parameters": {
+        "type": "params",
+        "required": [
+          "repo",
+          "tag"
+        ],
+        "properties": {
+          "repo": {
+            "type": "string",
+            "description": "Repository identifier in format 'did:plc:.../repoName'"
+          },
+          "tag": {
+            "type": "string",
+            "description": "Name of tag, such as v1.3.0"
+          }
+        }
+      },
+      "output": {
+        "encoding": "*/*"
+      },
+      "errors": [
+        {
+          "name": "RepoNotFound",
+          "description": "Repository not found or access denied"
+        },
+        {
+          "name": "TagNotFound",
+          "description": "Tag not found"
+        },
+        {
+          "name": "InvalidRequest",
+          "description": "Invalid request parameters"
+        }
+      ]
+    }
+  }
+}
diff --git a/types/repo.go b/types/repo.go
index 0d4dca3e..c2d3dc6a 100644
--- a/types/repo.go
+++ b/types/repo.go
@@ -94,6 +94,10 @@ type RepoTagsResponse struct {
 	Tags []*TagReference `json:"tags,omitempty"`
 }
 
+type RepoTagResponse struct {
+	Tag *TagReference `json:"tag,omitempty"`
+}
+
 type RepoBranchesResponse struct {
 	Branches []Branch `json:"branches,omitempty"`
 }
-- 
2.51.2