diff --git a/Cargo.toml b/Cargo.toml
index 3b3e004..1d947c0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,6 +8,7 @@ edition = "2021"
 [dependencies]
 anyhow = "1.0"
 lazy_static = "1.4.0"
+string-builder = "0.2.0"
 
 [dev-dependencies]
 base64 = "0.21.4"
diff --git a/src/bipack_sink.rs b/src/bipack_sink.rs
index a048637..de7a753 100644
--- a/src/bipack_sink.rs
+++ b/src/bipack_sink.rs
@@ -1,51 +1,115 @@
 use std::iter::Iterator;
-
-pub trait BipackSink {
-    fn put_u8(self: &mut Self, data: u8) -> &Self;
-
-    fn put_fixed_bytes(self: &mut Self, data: &[u8]) -> &Self {
-        for b in data { self.put_u8(*b); }
-        return self
-    }
-
-    fn put_u16(self: &mut Self, mut value: u16) -> &Self {
-        let mut result = [0u8; 2];
-        for i in (0..result.len()).rev() {
-            result[i] = value as u8;
-            println!(":: {} / {}", value, value as u8);
-            value = value >> 8;
-        }
-        self.put_fixed_bytes(&result)
-    }
-
-    fn put_u32(self: &mut Self, mut value: u32) -> &Self {
-        let mut result = [0u8; 4];
-        for i in (0..result.len()).rev() {
-            result[i] = value as u8;
-            println!(":: {} / {}", value, value as u8);
-            value = value >> 8;
-        }
-        self.put_fixed_bytes(&result)
-    }
-    fn put_u64(self: &mut Self, mut value: u64) -> &Self {
-        let mut result = [0u8; 8];
-        for i in (0..result.len()).rev() {
-            result[i] = value as u8;
-            println!(":: {} / {}", value, value as u8);
-            value = value >> 8;
-        }
-        self.put_fixed_bytes(&result)
-    }
-}
+use std::usize;
 
 const V0LIMIT: u64 = 1u64 << 6;
 const V1LIMIT: u64 = 1u64 << 14;
 const V2LIMIT: u64 = 1u64 << 22;
 
-impl BipackSink for Vec<u8> {
-    fn put_u8(self: &mut Self, data: u8) -> &Self {
-        self.push(data);
-        self
+pub trait IntoU64 {
+    fn into_u64(self) -> u64;
+}
+
+macro_rules! into_u64 {
+    ($($type:ident),*) => {
+        $(impl IntoU64 for $type {
+            fn into_u64(self) -> u64 {
+                self as u64
+            }
+        })*
+    };
+}
+
+into_u64!(u8, u16, u32, usize, u64);
+
+
+pub trait BipackSink {
+    fn put_u8(self: &mut Self, data: u8);
+
+    fn put_fixed_bytes(self: &mut Self, data: &[u8]) {
+        for b in data { self.put_u8(*b); }
+    }
+
+    fn put_var_bytes(self: &mut Self,data: &[u8]) {
+        self.put_unsigned(data.len());
+        self.put_fixed_bytes(data);
+    }
+
+    fn put_str(self: &mut Self,str: &str) {
+        self.put_var_bytes(str.as_bytes());
+    }
+
+    fn put_u16(self: &mut Self, mut value: u16) {
+        let mut result = [0u8; 2];
+        for i in (0..result.len()).rev() {
+            result[i] = value as u8;
+            value = value >> 8;
+        }
+        self.put_fixed_bytes(&result);
+    }
+
+    fn put_u32(self: &mut Self, mut value: u32) {
+        let mut result = [0u8; 4];
+        for i in (0..result.len()).rev() {
+            result[i] = value as u8;
+            value = value >> 8;
+        }
+        self.put_fixed_bytes(&result);
+    }
+    fn put_u64(self: &mut Self, mut value: u64) {
+        let mut result = [0u8; 8];
+        for i in (0..result.len()).rev() {
+            result[i] = value as u8;
+            value = value >> 8;
+        }
+        self.put_fixed_bytes(&result);
+    }
+
+    fn put_unsigned<T: IntoU64>(self: &mut Self, number: T) {
+        let value = number.into_u64();
+        let mut encode_seq = |ty: u8, bytes: &[u64]| {
+            if bytes.len() == 0 { self.put_u8(0); } else {
+                if bytes[0] as u64 > V0LIMIT { panic!("first byte is too big (internal error)"); }
+                self.put_u8((ty & 0x03) | ((bytes[0] as u8) << 2));
+                for i in 1..bytes.len() {
+                    self.put_u8(bytes[i] as u8);
+                }
+            }
+        };
+
+        if value < V0LIMIT {
+                encode_seq(0, &[value]);
+        }
+        else if value < V1LIMIT {
+            encode_seq( 1, &[value & 0x3F, value >> 6]);
+        }
+        else if value < V2LIMIT {
+            encode_seq(  2, &[value & 0x3f, value >> 6, value >> 14]);
+        }
+        else {
+            encode_seq(3, &[value & 0x3f, value >> 6, value >> 14]);
+            self.put_var_unsigned(value >> 22);
+        }
+    }
+
+    fn put_var_unsigned(self: &mut Self, value: u64) {
+        let mut rest = value;
+        loop {
+            let x = rest & 127;
+            rest = rest >> 7;
+            if rest > 0 {
+                self.put_u8((x | 0x80) as u8);
+            } else {
+                self.put_u8(x as u8)
+            }
+            if rest == 0 { break; }
+        }
+    }
+}
+
+
+impl BipackSink for Vec<u8> {
+    fn put_u8(self: &mut Self, data: u8) {
+        self.push(data);
     }
 }
 
diff --git a/src/bipack_source.rs b/src/bipack_source.rs
index ad2d431..ee0e97f 100644
--- a/src/bipack_source.rs
+++ b/src/bipack_source.rs
@@ -1,3 +1,5 @@
+use std::string::FromUtf8Error;
+
 /// Data source compatible with mp_bintools serialization. It supports
 /// fixed-size integers in rihgt order and varint ans smartint encodings
 /// separately.
@@ -50,6 +52,20 @@ pub trait BipackSource {
         self.smart_u64() as u16
     }
     fn smart_u32(self: &mut Self) -> u32 { self.smart_u64() as u32 }
+
+    fn fixed_bytes(self: &mut Self,size: usize) -> Vec<u8> {
+        let mut result = Vec::with_capacity(size);
+        for i in 0..size { result.push(self.u8()); }
+        result
+    }
+
+    fn var_bytes(self: &mut Self) -> Vec<u8> {
+        let size = self.smart_u64() as usize;
+        self.fixed_bytes(size)
+    }
+    fn str(self: &mut Self) -> Result<String, FromUtf8Error> {
+        String::from_utf8(self.var_bytes())
+    }
 }
 
 pub struct SliceSource<'a> {
diff --git a/src/lib.rs b/src/lib.rs
index 2f29f16..1fbf26a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,6 +3,7 @@
 
 mod bipack_source;
 mod bipack_sink;
+mod to_dump;
 
 pub fn add(left: usize, right: usize) -> usize {
     left + right
@@ -13,6 +14,7 @@ mod tests {
     use base64::Engine;
     use crate::bipack_sink::{BipackSink};
     use crate::bipack_source::{bipack_source, BipackSource, SliceSource};
+    use crate::to_dump::to_dump;
 
     #[test]
     fn fixed_unpack() {
@@ -34,6 +36,7 @@ mod tests {
         base64::engine::general_purpose::STANDARD_NO_PAD
             .decode_vec("BwLoA0IHBL+AAq7GDQ", &mut src)
             .expect("decoded vector");
+        // println!("{}", hex::encode(&src));
         let mut ss = bipack_source(&src);
         assert_eq!(7, ss.u8());
         assert_eq!(64000, ss.smart_u16());
@@ -48,8 +51,37 @@ mod tests {
         data.put_u16(64000);
         data.put_u32(66000);
         data.put_u64(931127140399);
-        // println!("-- {:?}", data.iter().map(|x| format!("{:0x}", x)).collect::<Vec<_>>());
-        assert_eq!("07fa00000101d0000000d8cb80a02f", hex::encode(&data).as_str());
-        // println!("data = {}", to_hex(&data));
+        assert_eq!("07fa00000101d0000000d8cb80a02f", hex::encode(&data));
+    }
+
+    #[test]
+    fn smart_pack() {
+        let mut data: Vec<u8> = Vec::new();
+        data.put_u8(7);
+        data.put_unsigned(64000u16);
+        data.put_unsigned(66000u32);
+        data.put_unsigned(931127140399u64);
+        // println!("?? {}", hex::encode(&data));
+        assert_eq!("0702e803420704bf8002aec60d", hex::encode(&data));
+    }
+
+    #[test]
+    fn pack_varbinaries_and_string() {
+        let mut data = Vec::<u8>::new();
+        data.put_str("Hello, rupack!");
+        println!("{}",to_dump(&data));
+        let mut src = bipack_source(&data);
+        assert_eq!("Hello, rupack!", src.str().unwrap());
+    }
+
+    #[test]
+    fn test_dump() {
+        for l in 1..64 {
+            let mut d2 = Vec::new();
+            for u in 0..l {
+                d2.push(u as u8);
+            }
+            println!("{}", to_dump(&d2));
+        }
     }
 }
\ No newline at end of file
diff --git a/src/to_dump.rs b/src/to_dump.rs
new file mode 100644
index 0000000..897daca
--- /dev/null
+++ b/src/to_dump.rs
@@ -0,0 +1,37 @@
+use string_builder::Builder;
+
+pub fn to_dump(data: &[u8]) -> String {
+    let mut offset = 0usize;
+    let mut counter = 0;
+    let mut result = Builder::default();
+
+    fn ascii_dump(result: &mut Builder, counter: usize, data: &[u8], offset: usize) {
+        for i in counter..16 { result.append("   "); }
+        result.append("|");
+        for i in 0..counter {
+            let b = data[offset - counter + i];
+            if b >= 32 && b <= 127 {
+                result.append(b as char)
+            } else {
+                result.append('.');
+            }
+        }
+        for i in counter..16 { result.append(' '); }
+        result.append("|\n");
+    }
+
+    while offset < data.len() {
+        if counter == 0 {
+            result.append(format!("{:04X} ", offset))
+        }
+        counter += 1;
+        result.append(format!("{:02x} ", data[offset]));
+        offset += 1;
+        if counter == 16 {
+            ascii_dump(&mut result, counter, data, offset);
+            counter = 0;
+        }
+    }
+    if counter != 0 { ascii_dump(&mut result, counter, data, offset); }
+    result.string().unwrap()
+}