feat: basic packfile retrieval

src/http.rs

@@ -0,0 +1,167 @@
+use std::io::Write;
+
+use anyhow::{Error, Result};
+use nom::AsBytes;
+use reqwest::Client;
+
+pub async fn clone(repo: &str) -> Result<(), Error> {
+    let (size, refs) = get_refs(repo).await?;
+
+    println!("Refs:");
+    for (sha1, name) in refs.iter() {
+        println!("{} {}", sha1, name);
+    }
+    println!("Downloaded file size: {}", size);
+
+    Ok(())
+}
+
+pub fn parse_refs(input: &[u8]) -> Result<Vec<(String, String)>> {
+    let mut refs = Vec::new();
+    let mut index: usize = 0;
+    loop {
+        if index >= input.len() {
+            break;
+        }
+        // pick the next 4 bytes and convert to u32 from hex
+        let mut bytes = [0; 4];
+        bytes.copy_from_slice(&input[index..index + 4]);
+
+        let hex_str = std::str::from_utf8(&bytes)?;
+        let res = usize::from_str_radix(hex_str, 16)?;
+
+        if res == 0 {
+            index += 4;
+            continue;
+        }
+
+        if input[index + 4] == b'#' {
+            index += res;
+            continue;
+        }
+
+        let mut sha1_bytes = [0; 40];
+        sha1_bytes.copy_from_slice(&input[index + 4..index + 44]);
+        let idx_0 = input[index + 45..index + res - 1]
+            .iter()
+            .position(|&x| x == 0);
+
+        let sha1 = std::str::from_utf8(&sha1_bytes)?;
+        let name = if let Some(idx_0) = idx_0 {
+            std::str::from_utf8(&input[index + 45..index + 45 + idx_0])?
+        } else {
+            std::str::from_utf8(&input[index + 45..index + res - 1])?
+        };
+
+        refs.push((name.to_string(), sha1.to_string()));
+
+        index += res;
+    }
+    Ok(refs)
+}
+
+pub async fn get_refs(repo_url: &str) -> Result<(usize, Vec<(String, String)>), Error> {
+    let info_refs_url = format!("{}/info/refs?service=git-upload-pack", repo_url);
+
+    let client = Client::new();
+    let response = client
+        .get(&info_refs_url)
+        .header("User-Agent", "git/2.30.0")
+        .send()
+        .await?;
+
+    response.error_for_status_ref()?;
+
+    let content = response.bytes().await?;
+    let refs = parse_refs(&content)?;
+
+    get_packfile(repo_url, refs).await
+}
+
+pub fn packet_line(data: &str) -> Vec<u8> {
+    let length = format!("{:04x}", data.len() + 4);
+    let mut line = Vec::new();
+    line.extend_from_slice(length.as_bytes());
+    line.extend_from_slice(data.as_bytes());
+    line
+}
+
+pub async fn get_packfile(
+    repo_url: &str,
+    refs: Vec<(String, String)>,
+) -> Result<(usize, Vec<(String, String)>), Error> {
+    let upload_pack_url = format!("{}/git-upload-pack", repo_url);
+
+    let mut payload: Vec<u8> = Vec::new();
+
+    payload.extend(packet_line("command=fetch").as_slice());
+    payload.extend(packet_line("agent=git/2.30.0").as_slice());
+    payload.extend(packet_line("object-format=sha1").as_slice());
+    payload.extend("0001".as_bytes());
+    payload.extend(packet_line("ofs-delta").as_slice());
+    payload.extend(packet_line("no-progress").as_slice());
+
+    for (_, sha1) in refs.iter() {
+        let want = format!("want {}\n", sha1);
+        payload.extend(packet_line(want.as_str()).as_slice());
+    }
+
+    payload.extend("0000".as_bytes());
+    payload.extend(packet_line("done").as_slice());
+
+    let client = Client::new();
+    let response = client
+        .post(&upload_pack_url)
+        .header("User-Agent", "git/2.30.0")
+        .header("Content-Type", "application/x-git-upload-pack-request")
+        .header("Accept-Encoding", "deflate")
+        .header("Accept", "application/x-git-upload-pack-result")
+        .header("Git-Protocol", "version=2")
+        .body(payload)
+        .send()
+        .await?;
+
+    response.error_for_status_ref()?;
+
+    let content = response.bytes().await?;
+    decode_git_response(content.as_bytes())?;
+
+    Ok((content.len(), refs))
+}
+
+fn decode_git_response(content: &[u8]) -> Result<(), Error> {
+    let mut cursor = 0;
+    let mut pack_data = Vec::new();
+
+    while cursor < content.len() {
+        let length_str = std::str::from_utf8(&content[cursor..cursor + 4])?;
+        cursor += 4;
+
+        let length = usize::from_str_radix(length_str, 16)?;
+        if length == 0 {
+            break;
+        }
+
+        let payload = &content[cursor..cursor + length - 4];
+        cursor += length - 4;
+
+        let side_band = payload[0];
+        let data = &payload[1..];
+
+        if side_band == 1 {
+            pack_data.extend(data);
+        } else if side_band == 2 {
+            println!("Progress: {}", std::str::from_utf8(data)?);
+        } else if side_band == 3 {
+            println!("Error: {}", std::str::from_utf8(data)?);
+        }
+    }
+
+    if !pack_data.is_empty() {
+        let mut packfile = std::fs::File::create("downloaded.pack")?;
+        packfile.write_all(&pack_data)?;
+        println!("Packfile saved as 'downloaded.pack'");
+    }
+
+    Ok(())
+}