feat: add duckdb functions for working with the narinfo dataset

duckdb/init.sql

@@ -0,0 +1,64 @@
+-- nixbase32: Encode binary blob to Nix base32 string
+--
+-- Nix uses a custom base32 alphabet: 0123456789abcdfghijklmnpqrsvwxyz
+-- (excludes e, o, t, u)
+--
+-- The encoding is little-endian
+-- Output length: ceil(input_bytes * 8 / 5)
+--   20 bytes (SHA1)   -> 32 characters
+--   32 bytes (SHA256) -> 52 characters
+--
+-- Usage:
+--   SELECT nixbase32(file_hash) FROM narinfos;
+--   SELECT nixbase32(unhex('e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'));
+CREATE OR REPLACE MACRO nixbase32(input) AS (
+    SELECT string_agg(
+        '0123456789abcdfghijklmnpqrsvwxyz'[
+            ((
+                (COALESCE(byte_arr[bit_pos // 8 + 1], 0) >> (bit_pos % 8)) |
+                (CASE WHEN (bit_pos % 8) > 3
+                      THEN COALESCE(byte_arr[bit_pos // 8 + 2], 0) << (8 - (bit_pos % 8))
+                      ELSE 0 END)
+            ) & 31) + 1
+        ],
+        '' ORDER BY n
+    )
+    FROM (
+        SELECT
+            n,
+            (out_len - 1 - n) * 5 as bit_pos,
+            byte_arr
+        FROM (
+            SELECT
+                ((octet_length(input)::bigint * 8 + 4) // 5)::bigint as out_len,
+                list_transform(
+                    generate_series(0::bigint, octet_length(input)::bigint - 1),
+                    i -> (instr('0123456789abcdef', lower(hex(input))[i*2+1]) - 1) * 16 +
+                         (instr('0123456789abcdef', lower(hex(input))[i*2+2]) - 1)
+                ) as byte_arr
+        ) params,
+        generate_series(0::bigint, out_len - 1) AS t(n)
+    )
+);
+
+-- narURL: Construct NAR URL path from file hash and compression type
+--
+-- Reconstructs the URL field from a narinfo, which is derived from:
+--   nar/<nixbase32(file_hash)>.nar[.<compression_ext>]
+--
+-- Compression mapping:
+--   '' or 'none' -> .nar
+--   'bzip2'      -> .nar.bz2
+--   'xz'         -> .nar.xz
+--   'zstd'       -> .nar.zstd
+--
+-- Usage:
+--   SELECT narURL(file_hash, compression) FROM narinfos;
+CREATE OR REPLACE MACRO narURL(file_hash, compression) AS (
+    'nar/' || nixbase32(file_hash) || '.nar' ||
+    CASE
+        WHEN compression = '' OR compression = 'none' THEN ''
+        WHEN compression = 'bzip2' THEN '.bz2'
+        ELSE '.' || compression
+    END
+);