add function to generate blob path from blob id

src/blobs.rs

@@ -0,0 +1,56 @@
+//! Blob utilities which do not require RPC calls.
+//!
+//! Offers the following functions:
+//!
+//! - [`get_blob_path()`]
+
+use crate::error::GolgiError;
+
+/// Lookup the filepath for a blob.
+///
+/// # Example
+///
+/// ```rust
+/// use golgi::blobs;
+///
+/// fn lookup_blob_path() -> Result<(), GolgiError> {
+///     let blob_ref = "&JlJHc9yeG1EpZA9fIPGLzUKDH0FeR39Ai57euhKT1G8=.sha256";
+///
+///     let blob_path = blobs::get_blob_path(blob_ref)?;
+///
+///     println!("{}", blob_path);
+///
+///     // 26/524773dc9e1b5129640f5f20f18bcd42831f415e477f408b9edeba1293d46f
+///
+///     Ok(())
+/// }
+/// ```
+pub fn get_blob_path(blob_id: &str) -> Result<String, GolgiError> {
+    let dot_index = blob_id.rfind('.').ok_or_else(|| {
+        GolgiError::SigilLink(format!(
+            "Invalid blob ID; no dot index was found: {}",
+            blob_id
+        ))
+    })?;
+
+    // obtain the base64 portion (substring) of the blob id
+    let base64_str = &blob_id[1..dot_index];
+
+    // decode blob substring from base64 (to bytes)
+    let blob_bytes = base64::decode_config(base64_str, base64::STANDARD)?;
+
+    // represent the blob bytes as hex, removing all unnecessary characters
+    let blob_hex = format!("{:02x?}", blob_bytes)
+        .replace('[', "")
+        .replace(']', "")
+        .replace(',', "")
+        .replace(' ', "");
+
+    // split the hex representation of the decoded base64
+    // this is how paths are formatted for the blobstore
+    // e.g. 26/524773dc9e1b5129640f5f20f18bcd42831f415e477f408b9edeba1293d46f
+    // full path would be: `/home/user/.ssb-go/blobs/sha256/26/524773dc...`
+    let blob_path = format!("{}/{}", &blob_hex[..2], &blob_hex[2..]);
+
+    Ok(blob_path)
+}

src/error.rs

@@ -34,9 +34,11 @@ pub enum GolgiError {
     Rpc(RpcError),
     /// Go-sbot error.
     Sbot(String),
+    /// SSB sigil-link error.
+    SigilLink(String),
     /// JSON serialization or deserialization error.
     SerdeJson(JsonError),
-    /// Error decoding typed ssb message from content.
+    /// Error decoding typed SSB message from content.
     ContentType(String),
     /// Error decoding UTF8 string from bytes
     Utf8Parse {
@@ -55,6 +57,7 @@ impl std::error::Error for GolgiError {
             GolgiError::Feed(ref err) => Some(err),
             GolgiError::Rpc(ref err) => Some(err),
             GolgiError::Sbot(_) => None,
+            GolgiError::SigilLink(_) => None,
             GolgiError::SerdeJson(ref err) => Some(err),
             GolgiError::ContentType(_) => None,
             GolgiError::Utf8Parse { ref source } => Some(source),
@@ -75,11 +78,12 @@ impl std::fmt::Display for GolgiError {
             // then have the core display msg be: "SSB RPC error: {}", context
             GolgiError::Rpc(ref err) => write!(f, "SSB RPC failure: {}", err),
             GolgiError::Sbot(ref err) => write!(f, "Sbot returned an error response: {}", err),
+            GolgiError::SigilLink(ref context) => write!(f, "SSB sigil-link error: {}", context),
             GolgiError::SerdeJson(_) => write!(f, "Failed to serialize JSON slice"),
             //GolgiError::WhoAmI(ref err) => write!(f, "{}", err),
             GolgiError::ContentType(ref err) => write!(
                 f,
-                "Failed to decode typed message from ssb message content: {}",
+                "Failed to decode typed message from SSB message content: {}",
                 err
             ),
             GolgiError::Utf8Parse { source } => {

src/lib.rs

@@ -69,6 +69,7 @@
 //! ```
 
 pub mod api;
+pub mod blobs;
 pub mod error;
 pub mod messages;
 pub mod sbot;