add a new tested context.new_blob_dir method to simplify writing out blob files

src/context.rs

@@ -1,5 +1,7 @@
 use std::collections::HashMap;
 use std::ffi::OsString;
+use std::fs;
+use std::io::Write;
 use std::path::{Path, PathBuf};
 use std::sync::{Arc, Condvar, Mutex, RwLock};
 
@@ -8,6 +10,7 @@ use libc::uintptr_t;
 use crate::chat::*;
 use crate::constants::*;
 use crate::contact::*;
+use crate::dc_tools::dc_derive_safe_stem_ext;
 use crate::error::*;
 use crate::events::Event;
 use crate::imap::*;
@@ -20,6 +23,7 @@ use crate::message::{self, Message};
 use crate::param::Params;
 use crate::smtp::*;
 use crate::sql::Sql;
+use rand::{thread_rng, Rng};
 
 /// Callback function type for [Context]
 ///
@@ -158,6 +162,41 @@ impl Context {
         self.blobdir.as_path()
     }
 
+    pub fn new_blob_file(&self, orig_filename: impl AsRef<str>, data: &[u8]) -> Result<String> {
+        // return a $BLOBDIR/<FILENAME> string which corresponds to the
+        // respective file in the blobdir, and which contains the data.
+        // FILENAME is computed by looking and possibly mangling the
+        // basename of orig_filename. The resulting filenames are meant
+        // to be human-readable.
+        let (stem, ext) = dc_derive_safe_stem_ext(orig_filename.as_ref());
+
+        // ext starts with "." or is empty string, so we can always resconstruct
+
+        for i in 0..3 {
+            let candidate_basename = match i {
+                // first a try to just use the (possibly mangled) original basename
+                0 => format!("{}{}", stem, ext),
+
+                // otherwise extend stem with random numbers
+                _ => {
+                    let mut rng = thread_rng();
+                    let random_id: u32 = rng.gen();
+                    format!("{}-{}{}", stem, random_id, ext)
+                }
+            };
+            let path = self.get_blobdir().join(&candidate_basename);
+            if let Ok(mut file) = fs::OpenOptions::new()
+                .create_new(true)
+                .write(true)
+                .open(&path)
+            {
+                file.write_all(data)?;
+                return Ok(format!("$BLOBDIR/{}", candidate_basename));
+            }
+        }
+        bail!("out of luck to create new blob file");
+    }
+
     pub fn call_cb(&self, event: Event) -> uintptr_t {
         (*self.cb)(self, event)
     }
@@ -438,6 +477,7 @@ pub fn get_version_str() -> &'static str {
 mod tests {
     use super::*;
 
+    use crate::dc_tools::*;
     use crate::test_utils::*;
 
     #[test]
@@ -475,6 +515,52 @@ mod tests {
         assert!(res.is_err());
     }
 
+    #[test]
+    fn test_new_blob_file() {
+        let t = dummy_context();
+        let context = t.ctx;
+        let x = &context.new_blob_file("hello", b"data").unwrap();
+        assert!(dc_file_exist(&context, x));
+        assert!(x.starts_with("$BLOBDIR"));
+        assert!(dc_read_file(&context, x).unwrap() == b"data");
+
+        let y = &context.new_blob_file("hello", b"data").unwrap();
+        assert!(dc_file_exist(&context, y));
+        assert!(y.starts_with("$BLOBDIR/data-"));
+
+        let x = &context.new_blob_file("hello", b"data.png").unwrap();
+        assert!(dc_file_exist(&context, x));
+        assert!(x.starts_with("$BLOBDIR"));
+
+        let y = &context.new_blob_file("hello", b"data.png").unwrap();
+        assert!(dc_file_exist(&context, y));
+        assert!(y.starts_with("$BLOBDIR/data-"));
+        assert!(y.ends_with(".png"));
+    }
+
+    #[test]
+    fn test_new_blob_file_long_names() {
+        let t = dummy_context();
+        let context = t.ctx;
+        let s = "12312312039182039182039812039810293810293810293810293801293801293123123";
+        let x = &context.new_blob_file(s, b"data").unwrap();
+        println!("blobfilename '{}'", x);
+        println!("xxxxfilename '{}'", s);
+        assert!(x.len() < s.len());
+        assert!(dc_file_exist(&context, x));
+        assert!(x.starts_with("$BLOBDIR"));
+    }
+
+    #[test]
+    fn test_new_blob_file_unicode() {
+        let t = dummy_context();
+        let context = t.ctx;
+        let s = "helloäworld.qwe";
+        let x = &context.new_blob_file(s, b"data").unwrap();
+        assert_eq!(x, "$BLOBDIR/hello-world.qwe");
+        assert_eq!(dc_read_file(&context, x).unwrap(), b"data");
+    }
+
     #[test]
     fn test_sqlite_parent_not_exists() {
         let tmp = tempfile::tempdir().unwrap();