internal/postgres: support for getting path info

Add GetPathInfo, a function that gets information about a path. The
main handler would call either GetPathInfo(path, "unknown", "latest")
if the incoming URL path had no "@", or GetPathInfo(path, "unknown",
version) if the incoming path looked like "foo@v".

Based on the returned path (or absence of one), it would decide whether
to call GetDirectory, GetPackage or GetModule.

Change-Id: Ifc09202d8ec110960e2c3bbaf04b79fc7a7c72df
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/728098
Reviewed-by: Julie Qiu <julieqiu@google.com>

1 files changed, 48 insertions, 1 deletions

diff --git a/internal/postgres/path.go b/internal/postgres/path.go
index 5a4cd238..b96fa87a 100644
--- a/internal/postgres/path.go
+++ b/internal/postgres/path.go
@@ -1,4 +1,4 @@
-// Copyright 2019 The Go Authors. All rights reserved.
+// Copyright 2020 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
@@ -8,11 +8,58 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"strings"
 
 	"github.com/lib/pq"
+	"golang.org/x/pkgsite/internal"
 	"golang.org/x/pkgsite/internal/derrors"
 )
 
+// GetPathInfo returns information about the "best" entity (module, path or directory) with
+// the given path. The module and version arguments provide additional constraints.
+// If the module is unknown, pass internal.UnknownModulePath; if the version is unknown, pass
+// internal.LatestVersion.
+//
+// The rules for picking the best are:
+// 1. Match the module path and or version, if they are provided;
+// 2. Prefer newer module versions to older, and release to pre-release;
+// 3. In the unlikely event of two paths at the same version, pick the longer module path.
+func (db *DB) GetPathInfo(ctx context.Context, path, inModulePath, inVersion string) (outModulePath, outVersion string, isPackage bool, err error) {
+	defer derrors.Wrap(&err, "DB.GetPathInfo(ctx, %q, %q, %q)", path, inModulePath, inVersion)
+
+	var constraints []string
+	args := []interface{}{path}
+	if inModulePath != internal.UnknownModulePath {
+		constraints = append(constraints, fmt.Sprintf("AND m.module_path = $%d", len(args)+1))
+		args = append(args, inModulePath)
+	}
+	if inVersion != internal.LatestVersion {
+		constraints = append(constraints, fmt.Sprintf("AND m.version = $%d", len(args)+1))
+		args = append(args, inVersion)
+	}
+	query := fmt.Sprintf(`
+		SELECT m.module_path, m.version, p.name != ''
+		FROM paths p
+		INNER JOIN modules m ON (p.module_id = m.id)
+		WHERE p.path = $1
+		%s
+		ORDER BY
+			m.version_type = 'release' DESC,
+			m.sort_version DESC,
+			m.module_path DESC
+		LIMIT 1
+	`, strings.Join(constraints, " "))
+	err = db.db.QueryRow(ctx, query, args...).Scan(&outModulePath, &outVersion, &isPackage)
+	switch err {
+	case sql.ErrNoRows:
+		return "", "", false, derrors.NotFound
+	case nil:
+		return outModulePath, outVersion, isPackage, nil
+	default:
+		return "", "", false, err
+	}
+}
+
 type dbPath struct {
 	id              int64
 	path            string