topic "Design Notes";
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[{_} 
[s2; Design Notes&]
[s3; Table of Contents&]
[s0; &]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#1^ 1. Overview]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#2^ 2. Architectural 
Model]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#3^ 3. Execution 
Model]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#4^ 4. State Model]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#5^ 5. Error Handling 
Strategy]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#6^ 6. Threading 
Model]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#7^ 7. Memory Model]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#8^ 8.  Identity 
`& RTTI]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#9^ 9. Subsystem 
Responsibilities]&]
[s0; [^topic`:`/`/Core`/SSH`/srcdoc`/Design`_en`-us`#10^ 10. Design 
Principles]&]
[s9;^`#11^ &]
[s3;:1: 1. Overview&]
[s5; The SSH package is a layered, RAII`-driven wrapper around libssh2, 
designed to integrate naturally with the U`+`+ ecosystem. &]
[s5; Its goals: &]
[s5;l192;i150;O0;~~~0; Provide a unified object`-oriented SSH abstraction&]
[s5;l192;i150;O0;~~~0; Preserve libssh2’s flexibility without exposing 
its procedural complexity&]
[s5;l192;i150;O0;~~~0; Support both GUI and console applications&]
[s5;l192;i150;O0;~~~0; Be cross`-platform (POSIX `+ Windows)&]
[s5;l192;i150;O0;~~~0; Support multithreading&]
[s5;l192;i150;O0; Follow U`+`+ idioms (pick semantics, Event, RTTI, 
memory manager)&]
[s5; At the center of the architecture is the [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Base`_en`-us`#Upp`:`:Ssh`:`:class^@(0.0.255) S
sh ]base class (the “core” abstraction). &]
[s3;:2: 2. Architectural Model&]
[s22; 2.1 Layered Design&]
[s6; [@(0.0.255)1 Ssh (Core)]&]
[s6; [@(0.0.255)1  ├── SshSession]&]
[s6; [@(0.0.255)1  │    ├── SshChannel]&]
[s6; [@(0.0.255)1  │    │    ├── Scp]&]
[s6; [@(0.0.255)1  │    │    ├── SshExec]&]
[s6; [@(0.0.255)1  │    │    ├── SshShell]&]
[s6; [@(0.0.255)1  │    │    └── SshTunnel]&]
[s6; [@(0.0.255)1  │    └── SFtp]&]
[s6; [@(0.0.255)1  │         └── SFtpStream]&]
[s6; [@(0.0.255)1  └── SshHosts ]&]
[s22; 2.2 Responsibilities by Layer&]
[s5; The [C^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Base`_en`-us`#Upp`:`:Ssh`:`:class^@5 S
sh][^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Base`_en`-us`#Upp`:`:Ssh`:`:class^  
]class provides: &]
[s5;l192;i150;O0; State machine&]
[s5;l192;i150;O0; Error handling&]
[s5;l192;i150;O0; Timeout handling&]
[s5;l192;i150;O0; Abort support&]
[s5;l192;i150;O0; Thread synchronization&]
[s5;l192;i150;O0; Event`-driven wait loop&]
[s5;l192;i150;O0; Common diagnostics/tracing&]
[s5;l192;i150;O0; Polymorphic base (RTTI`-enabled)&]
[s5; It encapsulates: &]
[s5;l192;i150;O0; LIBSSH2`_SESSION`*&]
[s5;l192;i150;O0; Socket state&]
[s5;l192;i150;O0; Timing state&]
[s5;l192;i150;O0; Error state&]
[s5;l192;i150;O0; Status flags (IDLE, WORKING, FAILED, ABORTED)&]
[s5; It does [* not] represent a concrete SSH entity. It represents 
the execution model. &]
[s3;:3: 3. Execution Model&]
[s22; 3.1 Cooperative Run Loop&]
[s5; Core execution is handled by: &]
[s7; [*@(0.0.255) bool] Ssh[@(0.0.255) `::]Run(Gate[@(0.0.255) <>`&`&] fn, 
[*@(0.0.255) bool] abortable)&]
[s5; Design intent: &]
[s5;l192;i150;O0; Wrap libssh2’s non`-blocking behavior&]
[s5;l192;i150;O0; Centralize timeout and abort checks&]
[s5;l192;i150;O0; Serialize critical SSH operations&]
[s5;l192;i150;O0; Ensure proper socket direction handling&]
[s5; Flow: &]
[s5;l192;i150;O0; Set status `= WORKING&]
[s5;l192;i150;O0; Record start time&]
[s5;l192;i150;O0; Repeatedly:&]
[s5;l416;i150;O0; Validate timeout&]
[s5;l416;i150;O0; Validate abort&]
[s5;l416;i150;O0; Validate socket state&]
[s5;l416;i150;O0; Lazily initialize session&]
[s5;l416;i150;O0; Execute user`-provided operation&]
[s5;l416;i150;O0; Call Wait() if libssh2 indicates blocking&]
[s5;l192;i150;O0; Transition to IDLE or FAILED&]
[s5; This abstracts libssh2’s EAGAIN`-style state machine into 
a higher`-level loop.&]
[s22; 3.2 Wait Strategy&]
[s0;b20;t300; &]
[s7; void Ssh`::Wait()&]
[s5; Uses: &]
[s5;l192;i150;O0; libssh2`_session`_block`_directions()&]
[s5;l192;i150;O0; SocketWaitEvent&]
[s5;l192;i150;O0; WAIT`_READ / WAIT`_WRITE mask&]
[s5;l192;i150;O0; Configurable wait step&]
[s5; Design goals: &]
[s5;l192;i150;O0; Respect non`-blocking semantics&]
[s5;l192;i150;O0; Avoid busy looping&]
[s5;l192;i150;O0; Integrate cleanly with U`+`+ event loop&]
[s5;l192;i150;O0; Support both console and GUI contexts&]
[s3;:4: 4. State Model&]
[s5; Core states: &]
[s5;l192;i150;O0; IDLE&]
[s5;l192;i150;O0; WORKING&]
[s5;l192;i150;O0; FAILED&]
[s5;l192;i150;O0; ABORTED&]
[s5; Transitions:&]
[s5;l192;i150;O0;~~~0; IDLE → WORKING (Run begins)&]
[s5;l192;i150;O0;~~~0; WORKING → IDLE (Success)&]
[s5;l192;i150;O0;~~~0; WORKING → FAILED (Error)&]
[s5;l192;i150;O0;~~~0; WORKING → ABORTED (User abort)&]
[s5; Abort is cooperative:&]
[s5;l192;i150;O0; Sets status flag&]
[s5;l192;i150;O0; Next Run iteration throws&]
[s3;:5: 5. Error Handling Strategy&]
[s5; Errors are captured via: &]
[s5; -|[@(0.0.255)1 struct Error : Exc]&]
[s5; Properties: &]
[s5;l192;i150;O0; Numeric error code&]
[s5;l192;i150;O0; Descriptive message&]
[s5;l192;i150;O0; Propagated via exceptions&]
[s5;l192;i150;O0; Normalized into internal state via [C@(0.0.255) SetError()]&]
[s5; This ensures:&]
[s5;l192;i150;O0; Consistent error propagation&]
[s5;l192;i150;O0; Clean user`-facing API&]
[s5;l192;i150;O0; libssh2 error translation&]
[s5; All public operations return status via [C@(0.0.255)1 operator 
bool(), IsError(), GetError(), GetErrorDesc()]&]
[s3;:6: 6. Threading Model&]
[s5; Key aspects:&]
[s5;l192;i150;O0; Static global mutex protects critical operations&]
[s5;l192;i150;O0; Designed for multithreaded usage at object level&]
[s5;l192;i150;O0; Internal operations are serialized&]
[s5; This design ensures:&]
[s5;l192;i150;O0; No race conditions inside libssh2 calls&]
[s5;l192;i150;O0; Controlled concurrency model&]
[s5;l192;i150;O0; Predictable behavior under load&]
[s3;:7: 7. Memory Model&]
[s5;l192;i150;O0; RAII`-based lifecycle&]
[s5;l192;i150;O0; Pick semantics supported&]
[s5;l192;i150;O0; Compatible with U`+`+ memory manager&]
[s5;l192;i150;O0; Optional native malloc mode&]
[s5;l192;i150;O0; Object lifetime is deterministic.&]
[s5;l192;i150;O0; Resources (session, channel, socket) are released 
in destructors. &]
[s3;:8: 8. Identity `& RTTI&]
[s5; Supports:&]
[s5;l192;i150;O0; Polymorphic storage&]
[s5;l192;i150;O0; Runtime casting via [C@(0.0.255) To<T>()]&]
[s5;l192;i150;O0; Type checking via [C@(0.0.255) Is<T>()]&]
[s5; Design goal: safe polymorphism without losing performance. &]
[s0;H1;h(220)G &]
[s3;:9: 9. Subsystem Responsibilities&]
[s5; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Session`_en`-us`#Upp`:`:SshSession`:`:class^ S
shSession]&]
[s5;l192;i150;O0; Authentication&]
[s5;l192;i150;O0; Handshake&]
[s5;l192;i150;O0; Agent support&]
[s5;l192;i150;O0; Known hosts verification&]
[s5;l192;i150;O0; Proxy support&]
[s5; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Channels`_en`-us^ SshChannel]&]
[s5;l192;i150;O0; Abstract channel handling&]
[s5;l192;i150;O0; Shared channel lifecycle logic&]
[s5;l192;i150;O0; Derived specializations: &]
[s5;l416;i150;O0; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Channels`_en`-us`#Upp`:`:Scp`:`:class^ S
cp] → file transfer&]
[s5;l416;i150;O0; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Channels`_en`-us`#Upp`:`:SshExec`:`:class^ S
shExec] → command execution&]
[s5;l416;i150;O0; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Channels`_en`-us`#Upp`:`:SshShell`:`:class^ S
shShell] → interactive shell `+ X11&]
[s5;l416;i150;O0; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Channels`_en`-us`#Upp`:`:SshTunnel`:`:class^ S
shTunnel] → port forwarding&]
[s5; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_SFtp`_en`-us`#Upp`:`:SFtp`:`:class^ SFtp]&]
[s5;l192;i150;O0; Subsystem initialization&]
[s5;l192;i150;O0; Directory traversal&]
[s5;l192;i150;O0; File operations&]
[s5;l192;i150;O0; Stream interface ([^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_SFtpStream`_en`-us`#Upp`:`:SFtpStream`:`:class^ S
FtpStream])&]
[s5; [^topic`:`/`/Core`/SSH`/src`/Upp`_Ssh`_Hosts`_en`-us`#Upp`:`:SshHosts`:`:class^ Ss
hHosts]&]
[s5;l192;i150;O0;~~~0; Known host verification&]
[s5;l192;i150;O0;~~~0; Host fingerprint management&]
[s0;H1;h(220)G &]
[s3;:10: 10. Design Principles&]
[s5;l192;i150;O0; Non`-blocking core wrapped in controlled blocking 
loop&]
[s5;l192;i150;O0; RAII discipline&]
[s5;l192;i150;O0; Clear separation of session vs channel vs subsystem&]
[s5;l192;i150;O0; Cross`-platform behavior abstraction&]
[s5;l192;i150;O0; Debug traceability at object granularity&]
[s5;l192;i150;O0; Avoid leaking libssh2 procedural complexity to 
users]]