Add max_reverse_swap_amount docs

snippets/csharp/SendOnchain.cs

@@ -28,6 +28,22 @@ public class SendOnchainSnippets
         // ANCHOR_END: get-current-reverse-swap-min-max
     }
 
+    public void MaxReverseSwapAmount(BlockingBreezServices sdk)
+    {
+        // ANCHOR: max-reverse-swap-amount
+        try
+        {
+            var maxAmountResponse = sdk.MaxReverseSwapAmount();
+            Console.WriteLine(
+                $"Max reverse swap amount {maxAmountResponse.totalSat}");
+        }
+        catch (Exception)
+        {
+            // Handle error
+        }
+        // ANCHOR_END: max-reverse-swap-amount
+    }
+
     public void StartReverseSwap(BlockingBreezServices sdk, ReverseSwapPairInfo currentFees, uint feeRate)
     {
         // ANCHOR: start-reverse-swap

snippets/dart_snippets/lib/send_onchain.dart

@@ -17,6 +17,14 @@ void listCurrentFees({required ReverseSwapPairInfo currentFees}) {
   // ANCHOR_END: get-current-reverse-swap-min-max
 }
 
+Future<MaxReverseSwapAmountResponse> maxReverseSwapAmount() async {
+  // ANCHOR: max-reverse-swap-amount  
+  MaxReverseSwapAmountResponse maxAmount = await BreezSDK().maxReverseSwapAmount();
+  print("Max reverse swap amount: ${maxAmount.totalSat}");
+  // ANCHOR_END: max-reverse-swap-amount
+  return maxAmount;
+}
+
 Future<SendOnchainResponse> startReverseSwap({
   required int amountSat,
   required String onchainRecipientAddress,

snippets/go/send_onchain.go

@@ -25,6 +25,14 @@ func ListCurrentFees(currentFees breez_sdk.ReverseSwapPairInfo) {
 	// ANCHOR_END: get-current-reverse-swap-min-max
 }
 
+func MaxReverseSwapAmount() {
+	// ANCHOR: max-reverse-swap-amount
+	if maxAmount, err := sdk.MaxReverseSwapAmount(); err == nil {
+		log.Printf("Max reverse swap amount: %v", maxAmount.TotalSat)
+	}
+	// ANCHOR_END: max-reverse-swap-amount
+}
+
 func StartReverseSwap() {
 	// ANCHOR: start-reverse-swap
 	destinationAddress := "bc1.."

snippets/kotlin_mpp_lib/shared/src/commonMain/kotlin/com/example/kotlinmpplib/SendOnchain.kt

@@ -20,6 +20,17 @@ class SendOnchain {
         // ANCHOR_END: get-current-reverse-swap-min-max
     }
 
+    fun max_reverse_swap_amount(sdk: BlockingBreezServices) {
+        // ANCHOR: max-reverse-swap-amount
+        try {
+            val maxAmount = sdk.maxReverseSwapAmount()
+            // Log.v("Breez", "Max reverse swap amount: ${maxAmount.totalSat}")
+        } catch (e: Exception) {
+            // handle error
+        }
+        // ANCHOR_END: max-reverse-swap-amount
+    }
+
     fun start_reverse_swap(sdk: BlockingBreezServices, fees: ReverseSwapPairInfo) {
         // ANCHOR: start-reverse-swap
         val address = "bc1.."

snippets/python/src/send_onchain.py

@@ -18,6 +18,17 @@ def list_current_fees(current_fees):
     print("Maximum amount, in sats: ", current_fees.max)
     # ANCHOR_END: get-current-reverse-swap-min-max
 
+def max_reverse_swap_amount(sdk_services):
+    try: 
+        # ANCHOR: max-reverse-swap-amount     
+        max_amount = sdk_services.max_reverse_swap_amount()
+        print("Max reverse swap amount: ", max_amount.totalSat)
+        # ANCHOR_END: max-reverse-swap-amount
+        return max_amount
+    except Exception as error:
+        print(error)
+        raise
+
 def start_reverse_swap(sdk_services, current_fees,fee_rate):
     # ANCHOR: start-reverse-swap
     destination_address = "bc1.."

snippets/react-native/send_onchain.ts

@@ -22,6 +22,17 @@ const exampleListCurrentFees = (currentFees: ReverseSwapPairInfo) => {
     // ANCHOR_END: get-current-reverse-swap-min-max
 }
 
+const maxReverseSwapAmount = async () => {
+    // ANCHOR: max-reverse-swap-amount
+    const maxAmount = await maxReverseSwapAmount()
+
+    console.log(
+        `Max reverse swap amount: ${maxAmount.totalSat}`
+    )
+    // ANCHOR_END: max-reverse-swap-amount
+}
+
+
 const exampleSendOnchain = async (currentFees: ReverseSwapPairInfo) => {
     // ANCHOR: start-reverse-swap
     const onchainRecipientAddress = 'bc1..'

snippets/rust/src/send_onchain.rs

@@ -30,6 +30,21 @@ async fn list_current_fees(current_fees: ReverseSwapPairInfo) -> Result<()> {
     Ok(())
 }
 
+async fn max_reverse_swap_amount(sdk: Arc<BreezServices>) -> Result<()> {
+    // ANCHOR: max-reverse-swap-amount
+    let max_amount = sdk
+        .max_reverse_swap_amount()
+        .await?;
+
+    info!(
+        "Max reverse swap amount: {:?}",
+        max_amount.totalSat
+    );
+    // ANCHOR_END: max-reverse-swap-amount
+
+    Ok(())
+}
+
 async fn start_reverse_swap(
     sdk: Arc<BreezServices>,
     current_fees: ReverseSwapPairInfo,

snippets/swift/BreezSDKExamples/Sources/SendOnchain.swift

@@ -24,6 +24,14 @@ func ListCurrentFees(currentFees: ReverseSwapPairInfo) {
     // ANCHOR_END: get-current-reverse-swap-min-max
 }
 
+func MaxReverseSwapAmount(sdk: BlockingBreezServices) -> MaxReverseSwapAmountResponse? {
+    //  ANCHOR: max-reverse-swap-amount   
+    let maxAmount = try? sdk.MaxReverseSwapAmount()
+    print("Max reverse swap amount: \(String(describing: maxAmount?.totalSat))")
+    // ANCHOR_END: max-reverse-swap-amount
+    return maxAmount
+}
+
 func StartReverseSwap(sdk: BlockingBreezServices, currentFees: ReverseSwapPairInfo) -> SendOnchainResponse? {
     // ANCHOR: start-reverse-swap
     let destinationAddress = "bc1.."

src/guide/send_onchain.md

@@ -74,7 +74,7 @@ The reverse swap will involve two on-chain transactions, for which the mining fe
 automatically once the process is started, but the last two values above are these estimates to help you get a picture
 of the total costs.
 
-Fetching the fees also tells you what is the range of amounts you can send:
+Fetching the fees also tells you what is the range of amounts the service allows:
 
 <custom-tabs category="lang">
 <div slot="title">Rust</div>
@@ -142,7 +142,75 @@ Fetching the fees also tells you what is the range of amounts you can send:
 </section>
 </custom-tabs>
 
-Once you checked the fees are acceptable, you can start the reverse swap:
+In case you want to drain your channels you need to know the maximum sendable amount to an on-chain address:
+
+<custom-tabs category="lang">
+<div slot="title">Rust</div>
+<section>
+
+```rust,ignore
+{{#include ../../snippets/rust/src/send_onchain.rs:max-reverse-swap-amount}}
+```
+</section>
+
+<div slot="title">Swift</div>
+<section>
+
+```swift,ignore
+{{#include ../../snippets/swift/BreezSDKExamples/Sources/SendOnchain.swift:max-reverse-swap-amount}}
+```
+</section>
+
+<div slot="title">Kotlin</div>
+<section>
+
+```kotlin,ignore
+{{#include ../../snippets/kotlin_mpp_lib/shared/src/commonMain/kotlin/com/example/kotlinmpplib/SendOnchain.kt:max-reverse-swap-amount}}
+```
+</section>
+
+<div slot="title">React Native</div>
+<section>
+
+```typescript
+{{#include ../../snippets/react-native/send_onchain.ts:max-reverse-swap-amount}}
+```
+</section>
+
+<div slot="title">Dart</div>
+<section>
+
+```dart,ignore
+{{#include ../../snippets/dart_snippets/lib/send_onchain.dart:max-reverse-swap-amount}}
+```
+</section>
+
+<div slot="title">Python</div>
+<section>
+
+```python,ignore
+{{#include ../../snippets/python/src/send_onchain.py:max-reverse-swap-amount}}
+```
+</section>
+
+<div slot="title">Go</div>
+<section>
+
+```go,ignore
+{{#include ../../snippets/go/send_onchain.go:max-reverse-swap-amount}}
+```
+</section>
+
+<div slot="title">C#</div>
+<section>
+
+```cs,ignore
+{{#include ../../snippets/csharp/SendOnchain.cs:max-reverse-swap-amount}}
+```
+</section>
+</custom-tabs>
+
+Once you decided about the amount and checked the fees are acceptable, you can start the reverse swap:
 
 <custom-tabs category="lang">
 <div slot="title">Rust</div>